Bacteriological Investigations of Diphtheria 
in the United States. 
A Report in Behalf of the American Committee on 
Diphtheria to the Eighth International Congress 
of Hygiene and Demography, held in Buda- 
pest, September 1 to g, 1894. 
BY 
WILLIAM H. WELCH, M.D., 
PROFESSOR OF PATHOLOGY IN THE JOHNS HOPKINS UNIVERSITY, BALTIMORE. 
FROM 
THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES, 
October, 1894. Extracted from The American Journal of the Medical Sciences, October, 1894. 
BACTERIOLOGICAL INVESTIGATIONS OF DIPHTHERIA IN 
THE UNITED STATES. 
A Report in Behalf of the American Committee on Diphtheria1 
to the Eighth International Congress of Hygiene and Demo- 
graphy, held in Budapest, September 1 to 9, 1894. 
William H. Welch, M.D., 
PROFESSOR OF PATHOLOGY IN THE JOHNS HOPKINS UNIVERSITY, BALTIMORE. 
It is intended in this report to present the more important results of 
the bacteriological study of diphtheria by American investigators, so 
far as these results are believed to be of interest for the purposes of this 
Congress. 
The most extensive bacteriological researches on diphtheria in this 
country have been made by Prudden and Park in the Pathological and 
Bacteriological Laboratories of the College of Physicians and Surgeons, 
Columbia College, New York (Director, Dr, T. M. Prudden), and by 
Park (partly in co-operation with Beebe) under the Division of Path- 
ology, Bacteriology, and Disinfection, Health Department of New 
York (chief of this Division, Dr. Hermann M. Biggs); by Welch, 
Abbott, Booker, and Flexner in the Pathological Laboratory of the 
Johns Hopkins University and Hospital (Director, Dr. W. H. Welch) ; 
by Koplik, working in the Carnegie Laboratory, Bellevue Hospital 
Medical College (under the direction of Dr. E. K. Dunham); by 
Abbott, Ghriskey and Ravenel in the Laboratory of Hygiene, Univer- 
sity of Pennsylvania (under the direction of Drs. J. S, Billings and 
A. C. Abbott); by Councilman, Williams, Morse, Townsend, Wright 
and Emerson in Boston, chiefly in the Boston City Hospital, and in the 
Pathological Laboratory of the Harvard Medical School (Director, 
Dr. W. T. Councilman). The references to articles are given at the 
end of this paper. 
The writer is indebted for original abstracts of their work (some of it 
hitherto unpublished) and their preparation for this report, to Drs. Prud- 
den, Park, Koplik, Abbott, Ravenel, Booker, Morse, Wright, and Emer- 
son ; and he desires to express to these gentlemen his cordial thanks for their 
kind co-operation, and also to Dr. Councilman for procuring the abstracts 
1 This committee, of which Dr. John S. Billings is Chairman, was appointed by the Secretary 
General of the Eighth International Congress of Hygiene and Demography, together with 
similar committees in other countries, to report to the Congress upon various questions 
relating to diphtheria. To the writer was assigned the subject of this report. 2 
welch: bacteriology of diphtheria. 
of work done under his supervision. It was intended at first to publish 
seriatim these abstracts, but it is believed that a systematic presentation 
of the combined results under suitable headings will be more useful. 
The purposes and limits of this report permit the statement of only some 
of the results of American workers, and these often in much abbreviated 
form. The writer, whose part is only that of a referee, will make free 
use, often without further acknowledgment, of the words of the authors. 
The larger part of the investigations of Park reported in this paper 
are unpublished. This report embraces the results up to May, 1894. 
In accordance with the programme of the Congress, especial attention 
will be given in this report to the results thus far obtained in the United 
States as to the following points: 
The application and value of bacteriological methods in the diagnosis 
of diphtheria; the proportion of cases of pseudo-membranous iuflamma- 
tions of the throat and air-passages due to the Loeffler bacillus; the 
various localizations of the diphtheria bacillus; atypical forms of 
diphtheria, and false diphtheria; the persistence of the Loeffler bacillus 
in the throat after recovery from diphtheria ; the occurrence of this 
bacillus outside of persons affected with diphtheria; the characters of 
pseudo-diphtheria bacilli. 
Historical.—The first bacteriological study of pseudo-membranous 
inflammations of the throat by modern methods in this country was by 
Prudden in 1889. He studied by microscopical examination and cul- 
tures twenty-four cases diagnosticated as diphtheria in young children, 
most of them in New York hospitals in which the affection had assumed 
the character of an epidemic. In a few of these cases the pseudo- 
membranous inflammation occurred by itself, but in most of them it 
was associated with scarlatina, measles, or suppuration. In all but two 
of these cases he found a streptococcus, usually in large numbers in the 
local lesions and in small numbers in a few cases in the viscera. Loeffler’s 
bacillus was not found in any of this group of cases. 
Prudden has withdrawn the name streptococcus diphtheriie, originally 
applied by him to the streptococcus found in these cases, which did not 
appear to differ from the streptococcus pyogenes. It is clear that the 
group of cases first studied by Prudden were not cases of genuine 
diphtheria, but were for the most part cases of secondary pseudo-mem- 
branous inflammations, which are now known to be oftener due to a 
streptococcus than to the Loeffler bacillus. 
In February and March, 1891, Welch and Abbott published the 
results of the bacteriological examination of eight cases of primary 
diphtheria, in all of which the Loeffler bacillus was found. 
In April, 1891, Prudden published the results in twelve cases of 
diphtheria unassociated with complicating lesions, and found the bacillus 
of Loeffler in all but one. WELCH: BACTERIOLOGY OF DIPHTHERIA. 
3 
Since these first publications the number of cases of suspected or 
established diphtheria which have been examined bacteriologically in 
the United States, so as to be available for statistical analysis, has been 
between 6000 and 7000 (May, 1894). 
Several hundred of these cases were examined in hospitals, dispen- 
saries, and private practice, but by far the larger number were examined 
under the Health Department of the City of New York. Under the 
intelligent and efficient direction of Dr. Biggs the Health Department 
has entered upon an undertaking which, upon such a scale, is believed 
to be hitherto unparalleled, to wit: the systematic examination of all 
cases of suspected diphtheria (unless objection is made by the attending 
physician or except certain cases in which it is not deemed advisable 
to disturb the patient) occurring in New York—the study of the cul- 
tures thus obtained being made by Dr. William H, Park and Mr. 
Alfred Beebe, who are thoroughly trained and careful bacteriologists. 
Some of the results of this undertaking will be considered in this 
paper. 
All the bacteriological aspects of diphtheria and other pseudo-mem- 
branous inflammations of the throat, with the exception of systematic 
study of immunization and serum-therapy, have been investigated 
by the various American workers already mentioned. Attention, 
however, will not be given in this paper to the purely morphological 
and cultural characters of the diphtheria bacillus, except as they relate 
to the question of differentiation of the pseudo-diphtheria bacillus. 
Technique.—In general the methods of examination have been 
those usually employed, and only a few points need to be especially 
mentioned. 
To obtain the material for cover-slips and culture from the suspected 
throat, Park uses sterile cotton swabs made by wrapping firmly a small 
pledget of absorbent cotton around the roughened end of a thin, stiff 
steel rod six inches in length. These swabs placed in an equal number 
of glass tubes, plugged with cotton, are sterilized for one hour by dry 
heat at 150° C. A similar method is employed by Councilman and 
others in Boston. Koplik prefers, both to the cotton swab and to the 
ordinary platinum wire, especially for removing tonsillar plugs, a small 
sterilized thin scoop in the form of a long bent probe. 
All are agreed as to the superiority of Loeffler’s blood-serum mixture for 
making original cultures from the throat. The blood-serum mixture is 
now generally prepared by direct sterilization and solidification in the 
steam or hot-air sterilizer at a temperature a little below 100° C., instead 
of the old method of fractional sterilization at a lower temperature. 
The loss of transparency in the medium is compensated by the greater 
facility in preparation, and no difficulty is found in seeing the colonies 
after twelve to eighteen hours. Egg-albumen, as recommended by 4 
welch: bacteriology of diphtheria. 
Johnston, and urine agar were found by Park less satisfactory than 
blood-serum. 
While recognizing that the bacillus of diphtheria grows well on agar 
when planted from cultures on blood-serum or other media, and that the 
agar colonies are the most characteristic and best adapted for micro- 
scopical study, Park calls attention to the uncertainty of glycerin-agar 
as a medium for making original cultures from the exudate. This 
uncertainty is due not only to unavoidable variations in the composition 
of the beef-broth, and to the less luxuriant character of the growth of 
the bacillus diphtherise as compared with its coincident growth with 
other bacteria upon blood-serum, but also to the observation that when 
the bacilli diphtherise are few in number or have been affected by previ- 
ous application of antiseptics, they may fail to grow upon agar when 
blood-serum inoculated at the same time and with the same exudate 
presents growth of the bacilli. Of course, the use of antiseptics shortly 
before making the inoculation of the tube is likely to render the cultures 
useless. 
When it is desired to determine accurately the kinds of bacteria asso- 
ciated in the exudate with the diphtheria bacillus, especially the presence 
of streptococci, it is desirable not to rely upon blood-serum alone, but to 
make also agar plates from the exudate. 
In testing the virulence of diphtheria cultures emphasis is laid, in all 
of the later work, upon observing precautions which have been noted 
especially by Behring and by Escherich. Thus Koplik selects young 
guinea-pigs weighing from 350 to 450 grammes, and injects 0.1 to 0.5 cc. 
of a bouillon culture forty-eight hours old in the thermostat. The 
quantity injected should be taken from the full culture after shaking 
and not after pouring off the supernatant fluid from the deposit. Park 
also emphasizes the importance of selecting, if possible, young guinea- 
pigs and injecting j to I per cent., in special cases even 1 per cent., 
of the body-weight of a forty-eight hour bouillon culture grown at 
37° C. 
For ordinary diagnostic purposes cover-slip preparations and cultures 
are considered sufficient without awaiting the result of the animal ex- 
periment. In all of the cases both cover slip preparations and cultures 
were made, and in many also inoculation of guinea-pigs. 
Methods Adopted by the Health Department in New 
York.—Under the Division of Pathology, Bacteriology, and Disinfec- 
tion, of which the Director of the Bacteriological Laboratory is Dr. 
Hermann M. Biggs, and the Inspector of Diphtheria Dr. William H. 
Park, the Health Department of New York has organized a system 
which renders available to physicians throughout the city the bacterio- 
logical diagnosis of diphtheria, and which utilizes in the interests of 
preventive medicine the important discoveries relating to the causation WELCH: BACTERIOLOGY OF DIPHTHERIA. 
5 
and mode of spread of diphtheria. These efforts have met, for the 
most part, with hearty co-operation on the part of physicians. 
For carrying out this and similar work, a bacteriological laboratory 
has been equipped and competent bacteriologists and a force of physi- 
cians as inspectors are employed. Cultures are made, not only when 
specifically requested by physicians, but also when no objection is raised 
by the attending physicians, diphtheria being, of course, a notifiable dis- 
ease. Especial attention is given to examinations in boarding-houses, 
hotels, and tenement-houses. 
In general, cultures are not made for diagnosis from secondary cases 
in families where the first case was proven bacteriologically to be 
diphtheria, or in cases of croup in which tracheotomy or intubation has 
been performed, the knowledge to be gained by cultures in such cases 
being too slight to compensate for the disturbance of the patient. All 
such cases, and, in fact, all suspected cases in which cultures are not 
obtained, are regarded as diphtheria. Later cultures are, however, 
made to determine when the bacilli have disappeared and the premises 
are ready for disinfection. 
Indeed, especial importance is attached to these later cultures, for in 
view of an extensive research to determine the length of time during 
which diphtheria bacilli may persist in the throat, the Health Depart- 
ment has adopted the rule, “ That no person who has suffered from 
diphtheria shall be considered free from contagion until it has been 
shown by bacteriological examination, made after the disappearance of 
the membrane from the throat, that the throat secretions no longer con- 
tain the diphtheria bacilli, and that until such examinations have shown 
such absence all cases in boarding-houses, hotels, and tenement-houses 
must remain isolated and under observation. Disinfection of the 
premises, therefore, will not be performed by the department until ex- 
amination has shown the absence of the organisms.” Cultures are made 
also from the apparently healthy throats in an infected household for 
reasons which will appear later in this report. 
The culture-tubes may be inoculated by the attending physician, if 
he so desires; otherwise the cultures are made by the inspector of the 
district in which the case occurs. The outfits for making the cultures, 
consisting of a box containing a tube of blood-serum and a steril- 
ized swab in a test-tube, are distributed to about forty stations at con- 
venient points throughout the city, these being mostly druggist shops. A 
list of these stations is published, at which physicians can obtain the 
outfit free of cost. 
Printed directions for making the cultures in suspected cases of diph- 
theria are supplied with the outfit, and are as follows: 
“The patient should be placed in a good light, and, if a child, pro- 
perly held. In cases where it is possible to get a good view of the throat, 6 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
depress the tongue and rub the cotton swab gently, but freely, against 
any visible exudate. 
“ In other cases, including those in which the exudate is confined to 
the larynx, avoiding the tongue, pass the swab far back, and rub it freely 
against the mucous membrane of the pharynx and tonsils. Without 
laying the swab down, withdraw the cotton plug from the culture-tube, 
insert the swab, and rub that portion of it which has touched the 
exudate gently but thoroughly all over the surface of the blood-serum. 
Do not push the swab into the blood-serum, nor break the surface in 
any way. Then replace the swab in its own tube, plug both tubes, put 
them in the box, and return the culture outfit at once to the station 
from which it was obtained. 
“A report will be forwarded the following morning by mail, or can 
be obtained by telephone, after 12 noon.” 
There follows a list of the stations from which the culture-outfits can 
be obtained free of cost. 
The inoculated tubes and swabs are sent from the stations to collecting 
depots, whence they are taken by the collectors on the same day to the 
laboratory. There is filled out and returned with the cultures a printed 
form giving the name and address of the attending physician and of the 
maker of the culture, the date, the name, age, and address of the patient, 
the clinical diagnosis, various details relating to the supposed causation, 
the duration and character of the disease, the use of antiseptic applica- 
tions, and a statement as to whether the inoculation was satisfactory. 
Another printed form is to be filled out for later cultures. 
From time to time explanatory circulars as to the character and re- 
sults of the work and the rules adopted by the department are issued to 
physicians. 
There are printed forms to be filled out in reporting to physicians the 
results of the cultures; one form is for cases in which diphtheria bacilli 
are found; another is for cases in which the bacilli once present have 
disappeared, and on this is the statement that the case is ready for dis- 
infection, if other circumstances allow ; a third form is for cases in which 
the cultures do not show the presence of diphtheria bacilli; and a fourth 
in the case of cultures 'which do not permit an exact bacteriological 
diagnosis with a statement of reasons for the failure, and, if need be, 
another culture is requested. 
Specimens of these various printed forms accompany this paper for 
the inspection of those attending the Congress. 
The results thus far obtained by this system have been satisfactory. 
From May 4, 1893, to May 4, 1894, 5611 cases of suspected diphtheria 
were subjected to bacteriological examination, some of the results of 
which will be stated later in this report. 
As to the reliance to be placed upon a culture in making a diagnosis, welch: bacteriology of diphtheria. 
7 
Park states, as the result of the very large experience accumulated by 
the Health Department, “ The examination by a competent bacteriologist 
of the bacterial growth in a blood-serum tube which has been properly 
inoculated and kept for fourteen hours at the body temperature can be 
thoroughly relied upon in cases where there is visible membrane in the 
throat, if the culture is made during the period in which the membrane 
is forming, and no antiseptic, especially no mercurial solution, has lately 
been applied. In cases in which the disease is confined to the larynx 
or bronchi, surprisingly accurate results can be obtained from culture, 
but in a certain proportion of cases no diphtheria bacilli will be found 
in the first culture, and yet will be abundantly present in later cultures. 
We believe, therefore, that absolute reliance for a diagnosis cannot be 
placed upon a single culture from the pharynx in purely laryngeal 
cases. The apparent mistakes, however, have been few. Cultures can- 
not be certainly relied upon after the membrane begins to disappear.” 
The great majority of physicians desire cultures to be made and ap- 
preciate the value of an accurate diagnosis. Cases which are proved 
not to be diphtheria are not required to be isolated and are not kept 
under supervision by the Department; until such proof, however, sus- 
picious cases are treated as diphtheria. 
The duration of the period of isolation and the time for disinfection 
are determined by the bacteriological examination in accordance with 
the rule already quoted. The increased value of statistics as to the dis- 
tribution, prevalence, mode of spread, clinical characters, mortality, 
and treatment of diphtheria when the diagnosis is based upon a bacterio- 
logical examination, requires no especial emphasis. Some of the scien- 
tific results which have been obtained by Dr. Park and Mr. Beebe from 
this immense material will be mentioned later in this article. 
Proportion of Cases op Suspected Diphtheria Proved by 
Bacteriological Examination to be True Diphtheria.—There are 
several points to be considered in estimating the value of statistics upon 
this point. The character of the cases selected for examination, whether 
wholly characteristic or less characteristic of diphtheria, will be of de- 
cisive influence. The degree of suspicion in a given case may be very 
slight, or one physician may consider the case highly suspicious or 
certain, and another may regard it as very doubtful or certainly not 
diphtheria. 
It is particularly in the doubtful cases that a bacteriological examina- 
tion is desired and is of the most importance. Diphtheria may occur 
without any false membrane and as an angina or tonsillitis of very mild 
character. 
In statistics based upon the statements of a large number of physi- 
cians as to the character of a local exudate it doubtless may happen 
that simple pultaceous and purulent exudates may be mistaken for 8 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
genuine fibrinous exudates. The inclusion of cases of pseudo-mem- 
branous angina, occurring in scarlet fever or other diseases, or even 
during the prevalence of scarlet fever, will influence the statistical result. 
Special local conditions, such as the selection of cases exclusively from 
children’s hospitals, and probably the time of year, may likewise have 
an influence upon the result. The care with which the cultures and 
cover-slip preparations are made and examined, the period of the disease 
at which they are made, the previous local application of antiseptics, 
are factors which will influence the result. 
These considerations (and still others might be mentioned) may render 
the statistics of different observers not strictly comparable, and they 
indicate that some statistics are likely to be more accurate and valuable 
than others. 
We owe to Park and to Morse the most extensive statistics as to the 
subject now under consideration. In his first published series Park ex- 
amined 140 pseudo-membranous cases uncomplicated with scarlet fever, 
in which the clinical diagnosis of probable diphtheria had been made. 
He found the Loetfler bacillus in 54 cases (39 per cent.). Of the 86 re- 
maining cases the membrane was confined to the tonsils in 58, and these 
latter were all mild. 
In his second published series, 104 uncomplicated cases were exam- 
ined and the Loetfler bacillus was found in 73 (70 per cent.). Dr. Park has 
kindly furnished the writer his later, as yet unpublished, statistics (partly 
in co-operation with Beebe), which will be included in a report to the 
Board of Health of New York. In this third series, 5611 cases or 
suspected diphtheria occurring in New York during the year ending 
May 4, 1894, were examined bacteriologically. A few of these cases 
complicated scarlet fever, but the precise number of such cases is not 
stated. The Loetfler bacillus was found in 3255 cases (58 per cent.), and 
was absent in 1540 cases (27 per cent.). In 816 cases, although no 
diphtheria bacilli were found in the cultures, yet either because the 
cultures were made after the fourth day of the disease, or because the 
exudate was imperfectly obtained from the throat, or because the cul- 
ture media had become contaminated or were too dry, the cases were 
considered to be of a doubtful nature as far as the bacteriological 
examination was concerned. If the doubtful cases be thrown out, which, 
however, it is hardly fair to do, as most of them are considered by Park 
not to have been diphtheria, we have, in 4795 cases of suspected diph- 
theria, about 68 per cent, of cases of true diphtheria, and 32 per cent, 
which were not diphtheria. 
Morse found, in 301 cases without scarlet fever admitted to the diph- 
theria ward of the Boston City Hospital, the Loetfler bacillus in 217 
(72 per cent.). 
If we add all of the cases of suspected diphtheria in Park’s and welch: bacteriology of diphtheria. 
9 
Morse’s statistics we have 6156 cases, of which 3599, or 58.5 per cent., 
were proved bacteriologically to be true diphtheria. If we reject from 
Park’s third series the cases in which the bacteriological examination was 
unsatisfactory we have 5340 cases, of which 67.5 per cent, were cases ot 
true diphtheria. 
Park’s first series was remarkable on account of the small percentage 
of cases of true diphtheria. The examinations were made in February 
and March, and scarlet fever was very prevalent, diphtheria less so. 
His experience at this time he considers to have been exceptional, and 
it has not been repeated. His own conclusion is, from his later observa- 
tions, that about 60 per cent, of the cases of suspected diphtheria in New 
York are true, and about 40 per cent, are false, diphtheria. 
We are, of course, not to infer that only 60 per cent, of the cases 
which are considered by physicians to be undoubted diphtheria are really 
diphtheria, but that this is about the percentage of cases of genuine 
diphtheria in the pseudo-membranous inflammations of the throat in 
which there is more or less suspicion of diphtheria. 
Upon each blank sent with a culture-tube by the Health Department 
of New York, a space is left for the voluntary recording of the clinical 
diagnosis by the physician. In 1210 cases of true diphtheria the physi- 
cian’s diagnosis was recorded. In 1011 the case was considered on 
clinical grounds to be diphtheria, in 102 to be doubtful, and in 87 to be 
probably false diphtheria. In 675 cases in which the diphtheria bacilli 
were absent a diagnosis of diphtheria was made in 50, the rest being all 
considered to be in doubt. 
In this connection Park says: “ The cases which present the charac- 
teristic appearances of well-developed diphtheria regularly contain in 
the pseudo-membranes abundant diphtheria bacilli. It is the slightly 
developed cases in which a culture is most needed. Here without cul- 
tures we need to go more by the history of exposure than the appearance 
of the case. In a family where an undoubted case of diphtheria existed, 
any form of sore throat, with or without exudate, in a child or adult, 
would be probably a case of diphtheria, while a similar-appearing ton- 
sillitis or pharyngitis in a person who had not been exposed to diph- 
theria would be, in all probability, a case of ordinary non-diphtheritic 
throat inflammation,” In only about one-half of the cases of diphtheria 
examined by the Health Department of New York did careful inquiry 
reveal any connection with other diphtheria cases. 
The statistics which have been cited are based upon the examination 
of pseudo-membranous inflammations of the throat and air-passages 
mostly uncomplicated with scarlet fever. 
Of particular significance is the outcome of Morse’s study: that in no 
less than 28 per cent, of the cases admitted to the diphtheria ward of 
the Boston City Hospital, diphtheria bacilli were not found. 10 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
Membranous Croup.—Welch and Abbott, Booker, Williams, and 
others have reported cases of diphtheria in which the pseudo-membrane 
was confined to the larynx and lower air-passages. In Park’s statistics 
there are 286 cases (283 children and 3 adults) in which the membrane 
was entirely or chiefly confined to the larynx or bronchi. In the cultures 
from 229 of these the Loeffler bacillus was found, and 167 of these 229 
cases showed no pseudo-membrane or exudate above the larynx, while in 
the remaining 62, although the larynx was mainly involved, there was 
also some membrane or exudate present on the tonsils or pharynx. In the 
remaining 57 no diphtheria bacilli were found, but of these, the cultures 
in 17 were unsatisfactory, leaving the bacteriological diagnosis doubtful. 
In the 40 cases in which the diphtheria bacilli were absent the disease 
was confined to the larynx or bronchi in 27, while more or less exudate 
or membrane was present on the tonsils or pharynx in 13. Of the cases 
of membranous croup in New York, therefore, at least 80 per cent, are 
diphtheria and only 14 per cent, were undoubtedly not diphtheritic. 
Cases of membranous croup were observed to be the origin of cases of 
characteristic pharyngeal diphtheria. 
The comparatively small number of laryngeal cases examined is 
accounted for by the custom of the department inspectors not to make 
cultures in cases which have been intubated or which seem so sick that 
the family might think injury had been done by inserting the swab. 
In a personal communication Dr. Park writes that he has no doubt 
as to the occurrence of non-diphtheritic pseudo-membranous laryngitis. 
He speaks of two cases in which the microscopical examinations and 
cultures made both during life and after death showed no diphtheria 
bacilli, but streptococci were present. Booker has reported such a case 
complicating measles. 
Fibrinous Rhinitis; Nasal Diphtheria.—Park reports 10 cases 
of fibrinous rhinitis in all of which the Loeffler bacillus was found. All 
were typical and of the usual benign character. In 9 the membrane 
was confined to the nose, and in one there was also slight fibrinous exu- 
date on the tonsils. Only the 6 cases in his first series are reported in 
detail. In 4 the Loeffler bacillus was associated with streptococci and 
in 2 with staphylococci. The virulence of the diphtheria bacillus was 
tested in 5 cases. The bacillus from one case killed a guinea-pig in 
four days; those from two cases in five days, and those from two other 
cases rendered the guinea-pig sick, but the animals eventually recovered. 
In addition to this weakening of virulence Park found that the bacilli 
from the first six cases grew more feebly than usual both on blood- 
serum and agar, and died out in cultures sooner than usual. 
Abbott has published 3 cases of fibrinous rhinitis, and Ravenel, work- 
ing under Abbott’s direction, has kindly sent me an account of 2 addi- 
tional cases which he will publish. All of these 5 cases were of benign welch: bacteriology of diphtheria. 
11 
character, the membrane being confined to the nasal cavity. Two were 
in sisters in the same family. In all the Loeffler bacillus was present 
in the membrane; in 3 it was of the customary virulence, and in 2 it 
produced only local reaction, in large doses failing to kill even half- 
grown guinea-pigs. 
Townsend observed in 14 cases of diphtheria, mostly of mild char- 
acter, occurring in the Children’s Hospital in Boston, 7 cases in which 
the nose was affected. Of the latter, in 5 cases the disease was primarily 
nasal, the membrane being confined to the nose in 4. These 4 cases of 
primary and exclusively nasal diphtheria were mild. In all the Loeffler 
bacillus of customary virulence was found. He emphasizes the case 
with which these primary nasal cases may be overlooked if the mem- 
brane remains confined to the nose, the importance of a bacteriological 
examination in all suspicious cases of nasal discharge, the mild character 
of many of the cases, their resemblance by superficial examination in 
some cases to an ordinary coryza, and the danger of such cases as sources 
of infection. 
Park mentions an instance in which a child with only a slight nasal 
discharge, in which Loeffler bacilli were demonstrated, gave rise to 
diphtheria in four children, of whom two died. The first child came 
from a family in which there had been a case of diphtheria three weeks 
before. 
Clinically Atypical Diphtheria.—The most important bacteri- 
ological study of this subject has been made by Koplik, who has kindly 
furnished the following abstract of his work : 
The writer has for the past three years directed his attention chiefly 
to the study of those forms of*diphtheria wThich clinically do not pre- 
sent any of the classical local symptoms of the disease. The direct 
outcome of these studies has been to demonstrate how multiform diph- 
theria may be, from a clinical standpoint, in its various local manifesta- 
tions, The first series of studies was published in the New York 
Medical Journal, August 27, 1892, and Archives of Paediatrics, Septem- 
ber, 1892. In these papers the writer gave the results of studies of the 
following forms of diphtheria: 
A. Cases in which there is from the onset and through the whole 
course of the disease no local manifestation of membrane, either diffuse 
or punctate. These cases may be so exceedingly mild in their course as 
to simulate a simple catarrhal angina, or they may be accompanied not 
only by anginal symptoms, but laryngeal symptoms, such as croupy 
cough and croupy breathing. In the latter case, early in the disease, 
we find upon the most careful inspection of the fauces no signs of mem- 
brane ; later, this picture may persist, or there may appear punctate 
areas of membrane upon the tonsils or pillars of the fauces. The 
point of greatest moment, however, is that at first and for days the 
closest inspection of the fauces and epiglottis reveals no signs of mem- 
brane. The croupy cough and breathing reveals involvement of the 
larnyx. Where only the cough is manifest it is to be presumed that in 12 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
the larynx the condition is much like that found in the throat, an intense 
inflammation without membrane. 
It is, of course, impossible to establish the exact anatomical condi- 
tions. In these cases I have fixed the diagnosis of diphtheria by 
scrapings from the tonsil and fauces. The most dangerous of these 
cases in spreading infection are those which present symptoms of a mild 
catarrhal angina. The writer has published a series of cases occurring 
in the same family of children who presented these mild anginal symp- 
toms. They communicated their anginal diphtheria to one another. 
Some of the cases developed membrane (punctate, in other cases diffuse 
of fauces and larynx), resulting in fatal laryngeal stenosis. On the 
other hand, the writer has published a series of cases of children who 
presented all symptoms of acute catarrhal angina, with signs of lacunar 
amygdalitis. In these cases the croupy crough and breathing were not 
present. These were not diphtheritic. The only test is the bacterio- 
logical one. 
B. A class of cases in which the tonsils are covered by a pultaceous 
mass of exudate, and no consistent membrane.. These cases may or may 
not be true diphtheria. 
C. A large class of cases presenting punctate form of membrane; 
some of these spots of membrane may be isolated and minute on the 
tonsil; in some forms the specks of membrane are depressed in the sur- 
face of the tonsil. In other forms minute or larger ulcerations exist. 
These cases may be diphtheritic, and in the vast majority of cases are 
true diphtheria. In other cases we fail to find the Loeffier bacillus. 
D. The most important class of clinically atypical diphtherias are 
those cases which begin or even run their entire course with the clinical 
local picture of a typical lacunar or follicular amygdalitis. In my last 
paper, entitled “Acute Lacunar Diphtheria of the Tonsils” (New York 
Medical Journal, March 10, 1894) these cases are divided into groups. 
In the first group of cases the course of the disease is that of an ex- 
ceedingly mild lacunar or follicular amygdalitis. The fauces are 
injected, the tonsils are enlarged, there iS an indication here and there 
of a lacuna, by a yellow spot; the lymph-glands at the angle of the 
jaw may or may not be enlarged; the constitutional symptoms are 
almost nil. Extraction of the contents of the lacunae or follicles shows 
the presence of the bacillus diphtherise. 
In the second group of cases the tonsils are more inflamed, the 
lacunar plugs protrude from the tonsils in the form of soft fibrinous 
masses; the patients seem quite ill, as if suffering from a severe amyg- 
dalitis. In these cases also the lacunar plugs are found to contain the 
Klebs-Loeflier bacillus in almost pure culture. Here also glandular 
nodes are found at the angle of the jaw. The course of these cases clini- 
cally is interesting; some never develop membrane as a mass on the 
tonsils; others after the third day develop distinct thick confluent mem- 
brane on the tonsils. Others remain lacunar in the local tonsillar picture, 
but develop laryngeal diphtheria, with croupy cough and breathing. In 
this class the lymph nodes at the angle of the jaw may be much enlarged 
in packets, or not much above what is found in ordinary anginas. These 
cases may give rise to other cases in the same family in which the course of 
the disease is that of a simple lacunar amygdalitis, but which upon exami- 
nation prove to be true diphtheria. 
The third group of cases are those in which the disease begins with WELCH: BACTERIOLOGY OF DIPHTHERIA. 
13 
the picture of severe lacunar amygdalitis, but the prostration of the 
patient is exceedingly great; the temperature may be low. There is 
great glandular swelling at the angle of the jaw. After a few days the 
prostration is much greater; there appears nasal discharge, and small 
shreds of membrane are discharged from between the much swollen 
tonsils. The tonsils themselves are now covered with one continuous 
membrane, but here and there shreds are seen on the surface of the 
eroded tonsil. These cases are the septic lacunar diphtherias with 
nasal symptoms, and give a bad prognosis. 
In a series of 39 cases of acute lacunar or follicular inflammation of 
the tonsils, 12 were proven to contain the Loeffler bacilli in the depths 
of the tonsillar lacunae. Thus, fully one-third of the cases were diph- 
theria. It is not intended to draw any percentage conclusion from 
this, but it demonstrates how insidious an affection lacunar amygdalitis 
may be. (New York Medical Journal, March 10, 1894.) 
Diphtheria sine membrana has been observed also by several other 
American investigators. Reference has already been made to Park’s 
statement that any form of sore-throat in a person exposed to diphtheria 
is likely to be referable to the diphtheria bacillus. He says: “ Under 
diphtheria should be included all inflammations of mucous membranes 
due to the diphtheria bacillus of Loeffler. A case with an acute hyper- 
aemia of the raucous membrane in which the Loeffler bacilli are present 
is considered as truly a diphtheria as one with pseudo-membrane or 
exudate.” Only the bacteriological examination can determine the 
true character of these cases. It is to be borne in mind, as pointed out 
by Councilman, that the absence of the pseudo-membrane in the places 
where it is ordinarily found is not proof that it is not present elsewhere, 
perhaps in some place not accessible to examination. 
Other Localizations op the Diphtheria. Bacillus and its 
Distribution at Autopsies.—Councilman has found the diphtheria 
bacillus in one case of otitis media following diphtheria and in two cases 
of otitis media, without affection of the throat, in measles. Townsend 
observed a case in which an old tracheotomy wound was attacked and 
the disease spread to the bronchi, proving rapidly fatal, with demon- 
stration of the Loeffler bacillus. Park found diphtheria bacilli in two 
cases in wounds of the finger received by physicians in intubating 
children with diphtheria. In one case the bacilli persisted in the 
wound for six weeks. Wright (unpublished results communicated 
to the writer) has demonstrated the presence of this bacillus in exco- 
riated or ulcerated surfaces of the skin in 7 cases, in paronychia in 
1, in mastoid abscess in 1, in purulent conjunctivitis in 1—all in cases 
of diphtheria. At autopsy he cultivated the bacillus from the ecchy- 
motic mucous membrane of the stomach in 2 cases, and from oedematous 
tissue behind the oesophagus in 1. Wright also reports that in 10 out of 
14 autopsies in cases of diphtheria broncho-pneumonia was present, and 
that in 9 cases the Loeffler bacillus was found in the lung, and in the re- 14 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
maining case only the streptococcus. In 7 of the 9 pneumonias streptococci 
accompanied the Loeffler bacillus, as well as in two other lungs in which 
no pneumonia existed. In 3 or 4 pneumonias the diplococcus pneumoniae 
was also present. The staphylococcus pyogenes aureus was also met in 4 
pneumonias, once with the Loeffler bacillus and three times in company 
with all of the three bacteria just mentioned. Flexner has found the 
Loeffler bacillus in two broncho-pneumonias complicating diphtheria, 
and by microscopical examination of sections demonstrated Loeffler 
bacilli, mostly within leucocytes, in the broncho-pneumonic.exudate. In 
both cases the diplococcus pneumoniae was, however, the predominant 
organism. 
Howard has reported a case of acute ulcerative endocarditis (without 
diphtheria) with infarctions in the spleen and kidneys, in which, both 
by cultures and microscopical examination, bacilli indistinguishable 
morphologically and in cultures from the diphtheria bacillus, but devoid 
of virulence, were found abundantly and in pure culture in the valvular 
vegetations, the spleen, and the kidneys. 
As to the presence of the diphtheria bacillus in internal organs at 
autopsy Booker reports a case of diphtheritic laryngitis in which at 
autopsy Loeffler bacilli were found in the blood, spleen, and lungs. 
Wright has found this bacillus out of 14 cases dead of diphtheria in the 
lung in 13 cases (9 with broncho-pneumonia), in the liver in 3, in the 
spleen in 2, in the cervical or bronchial lymph-glands in 5, in the kidney 
in 1, in the blood in 1, and in the mesenteric lymph-glands in 2. In 7 
of these cases there was streptococcus septicamia and in 2 a similar 
poly-infection with the staphylococcus pyogenes aureus. Two of the 
autopsies showed no marked lesions of diphtheria in the throat or trachea, 
the nasal cavities not having been examined. Both yielded virulent 
Loeffler bacilli—in one from the cervical lymph-glands and in the other 
from the pharynx. In both the bacillus was found in the air-passages. 
The bacillus, with slight virulence, was found also in certain of the 
organs in 3 autopsies on cases apparently not dead of diphtheria. 
In guinea-pigs dead of experimental diphtheria, Wright found the 
diphtheria bacillus in the liver in 19 out of 155 cases, in the spleen in 
15 out of 152 cases, in the heart’s blood in 7 out of 153 cases, and in 
the kidney in 4 out of 151 cases. 
Both in these as well as in the human cases the bacilli were found in 
the organs in but very small numbers, as a rule. 
In three guinea-pigs the bacillus has been recovered by Wright from 
the seat of inoculation thirty-one to thirty-eight days after the date of 
inoculation. 
Abbott and Ghriskey have observed frequently after inoculation of 
diphtheria bacilli into the testicles, less frequently after subcutaneous 
inoculation, of guinea-pigs, small nodules in the omentum composed WELCH : BACTERIOLOGY OF DIPHTHERIA, 
15 
mostly of polynuclear leucocytes and containing the bacilli in large 
number. 
Welch and Flexner have described in detail the histological changes 
in experimental diphtheria, and have shown that these are characterized 
especially by widely distributed areas of cell death with nuclear frag- 
mentation. They have demonstrated that the local fibrinous exudate 
may be caused by dead, as well as living, diphtheria bacilli, and that 
the other lesions are referable to toxic products of the bacillus. 
Bacteria Associated with the Diphtheria Bacillus.—All of 
the investigators have found, as a rule, other bacteria associated with 
the Loeffler bacillus in the local exudates of diphtheria, although this 
bacillus is the only one which is constantly present. The most common 
associated micro-organism is the streptococcus pyogenes. Other bacteria 
which have been found are the regular buccal bacteria, the micrococcus 
lanceolatus, the staphylococcus albus and aureus, the bacillus coli com- 
munis (Morse), unnamed cocci and unnamed bacilli. Among these bacilli 
may be specified a short oval, slightly pointed bacillus, growing in long 
chains, running parallel to each, forming grayish-white colonies on agar not 
unlike those of the Loeffler bacillus. This bacillus was frequently en- 
countered by Welch and Abbott. Morse describes a short, motile, liquefy- 
ing bacillus and a non-raotile diplo-bacillus growing invisibly on potato 
and not growing on gelatin. The only associated bacteria which are 
believed to exert pathogenic action are the streptococci, the pyogenic sta- 
phylococci, the micrococcus lanceolatus, and a coccus observed by Koplik 
which he considers to be identical with that described by Roux and Yersin 
and by Martin. Differences, mostly of a minor character, have been noted 
both in morphology and cultural characters between the different strep- 
tococci, but they are not considered sufficient to establish definitely 
different species. 
It is regarded as established by all the investigators that the course 
and symptoms of diphtheria may be definitely influenced by these asso- 
ciated pathogenic bacteria, particularly by the most common of all, the 
streptococcus pyogenes. Cases of general streptococcus septicaemia 
accompanying diphtheria have been observed, especially by Councilman 
and his co-workers. Broncho-pneumonias, suppurations of lymph- 
glands and the so-called septic forms of diphtheria are attributed to 
these associated bacteria, especially to the streptococcus. It does not 
appear, however, either from the statistics of Park or of Morse, that the 
mortality is materially higher in cases of diphtheria in which the strep- 
tococcus is associated with the LoefHer bacillus than when the Loeffler 
bacillus is present without streptococci. In fact, the tables of Morse 
show a higher mortality when the Loeffler bacillus is associated with 
pathogenic staphylococci than with streptococci. Morse, however, does 
not attach decisive weight to this inference, as only in 25 cases did he 16 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
attempt a thorough differential study of all associated bacteria. Such 
study will always show the presence of other bacteria. In these 25 
cases he found the streptococcus in 19 cases (9 without other bacteria in 
culture, except the Loeffler bacillus, 6 with staphylococcus aureus or 
albus, or both), and staphylococcus aureus or albus in 10 cases (4 alone, 
except the Loeffler bacillus). The general mortality in these 25 cases 
was 56 per cent., the mortality in the cases with the Loeffler bacillus 
and streptococci alone, 33 per cent., with Loeffler bacillus and staphy- 
lococci alone, 66 per cent., and with Loeffler bacillus, streptococci, and 
staphylococci, 66 per cent. As Morse says : “ Statistics compiled from 
so small a number of cases are of little value.” A similar conclusion 
as to the greater harmfulness of staphylococci than of streptococci is 
reached by Morse, contrary to the generally accepted opinion, also from 
the analysis of his larger table of 400 cases (301 without scarlet fever) ; 
but he admits that the comparatively small number of cases in which 
the streptococcus was found associated with the Loeffler bacillus (191 
cases) may have been due to failure to recognize the minute, slow- 
growing colonies of streptococci in the twenty-four-hour blood serum 
tubes, and the arrangement of the cocci on cover-glass specimens alone 
is not decisive as to the diagnosis of staphylococci, which were found 
in 295 cases. A minute and careful differentiation of the bacterial 
species was attempted by Morse in only 25 cases. We cannot, there- 
fore, consider it established that staphylococci are more harmful than 
streptococci, especially as this inference is opposed to that of other in- 
vestigators, and as Morse doubtless often overlooked the presence of 
streptococci. 
Pseudo-Membranous Inflammations of the Throat in Scarlet 
Fever, Measles, and Typhoid Fever.—In an epidemic of scarlet 
fever in Baltimore at the time when the city was unusually free from diph- 
theria, one-half of the cases seen by Booker had pseudo-membranous 
affection of the throat. He has reported 11 cases of pseudo-membranous 
angina (2 fatal) complicating scarlet fever, and 1 case of similar angina 
without exanthem in a family three members of which had scarlatina. 
In all of these cases, as well as in 4 scarlatinal anginas without pseudo- 
membrane, Booker found streptococci as the predominant organisms, and 
in none was the Loeffler bacillus present. In one case croupous con- 
junctivitis due to streptococci was associated with the pseudo-membran- 
ous angina. The staphylococcus aureus was found in 11 cases without 
apparent influence on the severity of the case. No difference was ob- 
served between the early and the late pseudo-membranous anginas as 
regards the bacteria present. He attributes the absence of true diph- 
theria from so large a number of cases of scarlatina as due to the free- 
dom of the city from diphtheria at the time. Booker describes with much 
detail the morphological and biological characters of the streptococci WELCH: BACTERIOLOGY OF DIPHTHERIA. 
17 
found, and divides them into groups, but these details will not here be 
considered. 
Park in his first series of 159 cases reports 19 cases of pseudo-mem- 
branous inflammation of the throat complicating scarlatina. In 17 
streptococci predominated, and in only 2 were Loeffler bacilli present, 
these latter presenting diphtheritic laryngitis. Staphylococci were met 
in only a few cases. 
The experience in Boston, as reported by Williams and by Morse, has 
been exceptional in the large proportion of cases of true diphtheria com- 
plicating scarlet fever. Of 97 cases of scarlet fever in the Boston City 
Hospital, of which 35 came from two homes for children, reported by 
Williams, membranous throats were present in 35. Of these 12 were 
due to the Loeffler bacillus, and in 23 the Loeffler bacillus was not 
found. In the 23 pseudo-diphtheria cases the membrane was limited 
to the tonsils in 5 only, and in 3 it extended to the larynx. Of the 62 
cases of scarlet fever alone, 8 died (13 per cent.), of the cases of scarlet 
fever with diphtheria 6 died (50 per cent.), of the 23 cases of scarlet 
fever with pseudo-diphtheria 5 died (22 per cent.). In a previous series 
of 86 cases of scarlet fever, of which 19 were complicated with mem- 
branous throats, but no bacteriological examination was made, the 
mortality in the latter group was 47 per cent., while in the 67 cases 
without membranous throats only 4J per cent, died. 
In Morse’s paper are probably included some of the cases reported 
by Williams, as the observations of both are from the Boston City 
Hospital. Morse reports 99 cases of pseudo-membranous inflammation 
of the throat complicating scarlet fever. Of these 26 per cent. died. 
The Loeffler bacillus was found in 23, with a mortality of 43 per cent., 
and was not found in 76, with a mortality of 21 per cent. In the 
pseudo-diphtheric cases streptococci were present in 61, staphylococci 
(in 12 alone and in 57 with streptococci) in 69, and other bacteria in 3 
cases. Mention has already been made of the large number of staphy- 
lococcus cases in general in Morse’s statistics. 
It is the opinion of Morse, and of Councilman, under whose direction 
Morse worked, that the large proportion of cases of combined scarlatina 
and diphtheria was due to contagion in the hospital where the conditions 
were unfavorable for proper isolation. These unfavorable conditions 
will be remedied in the new hospital for infectious diseases now building. 
A few of the mixed cases, however, were admitted with double infection 
as shown by bacteriological examination at entrance. Most of the cases 
came from tenement-houses. In Williams’ cases the fact that 35 came 
from two public institutions may explain in part the large number of 
associated infections. 
In contrast with these results in Boston it is interesting to note the 
observations of Booker, already cited, at a time and place in which 18 
WELCH : BACTERIOLOGY OF DIPHTHERIA. 
diphtheria was notably absent. It is evident that the proportion of 
cases in which true diphtheria complicates scarlet fever depends largely 
upon local conditions, these relating to the prevalence of diphtheria and 
the opportunities for contagion. 
Booker reports three cases of pseudo-membranous inflammation 
accompanying measles. In all, streptococci and the staphylococcus 
aureus were found, and in none the Loetfler bacillus. These cases 
occurred during the same period as the scarlatinal cases, when the city 
was exceptionally free from diphtheria. In two cases the membrane 
was limited to the larynx, there being no visible exudate. One of these 
was fatal, and at the autopsy the whole larynx was covered by a tough, 
very loosely adherent, false membrane. Both microscopical examina- 
tion and cultures of the membrane after death, as well as those made 
from the pharynx during life, failed to show Loetfler bacilli. This case, 
therefore, is a particularly conclusive one of the occurrence of mem- 
branous laryngitis without diphtheria. The third case presented pseudo- 
membrane on the tonsils, pharynx and conjunctive. Streptococci pre- 
dominated with some colonies of the staphylococcus aureus. 
In Park’s first series of cases there is one case of laryngeal diphtheria 
accompanying measles. Loetfler bacilli were present. The child re- 
covered after intubation. In another case, in which there was mem- 
branous laryngitis without diphtheria bacilli in the pharynx, measles 
developed on the eighth day. Intubation had been performed and was 
followed by recovery. 
Williams reports one case of measles with diphtheria. This case, 
however, may be the same one as appears in Morse’s statistics, who 
reports four cases of measles with severe throat symptoms giving rise to 
the clinical diagnosis of diphtheria. One contained a few Loetfler 
bacilli and many staphylococci. Of these two died. Six cases had 
measles and scarlet fever together, but it does not appear that any of 
these had membranous throats. All recovered, and the Loetfler bacillus 
was not found in any. Streptococci were present in 5, staphylococci in 
2, and the diplococcus lanceolatus in 2. 
Of particular interest are four cases of typhoid fever complicated by 
diphtheria, reported by Morse. At least three of the cases developed 
diphtheria after admission to the hospital. One was a patient ill with 
typhoid fever in a private room. A nurse, several days after leaving 
the scarlet fever ward, had a sore-throat, and was put in the same room 
over night. On the discovery of the Loetfler bacillus in her throat the 
next day, the nurse was transferred to the diphtheria ward. Four days 
later the patient with typhoid fever developed sore-throat with mem- 
brane containing the Loetfler bacillus. The next day a typical scarlet- 
fever rash developed, which was followed by desquamation. She ulti- 
mately recovered. One of the four patients died. At the autopsy WELCH ; BACTERIOLOGY OF DIPHTHERIA. 
19 
were found lesions of typhoid fever with diphtheritic pharyngitis, ton- 
sillitis and laryngitis. Loeffler bacilli were demonstrated both intra vitam 
and post mortem. In addition, typhoid bacilli and general streptococcus 
infection were found in cultures after death. Wagner has already 
called attention to the greater frequency of pseudo-membranous affec- 
tions in typhoid fever when diphtheria is prevalent. 
Pseudo-diphtheria.—The name pseudo-diphtheria is used by Park, 
Williams, and others to designate pseudo-membranous inflammations of 
the throat and air-passages not caused by the bacillus of diphtheria. 
The name is, for several reasons, objectionable, but no convenient sub- 
stitute has been suggested. The term streptococcus diphtheritis fits most 
of the cases, but not all. The pseudo-diphtheria bacillus is not con- 
cerned in the causation of pseudo-diphtheria, or, if so, only in a very 
small number of cases. 
We have just seen that the great majority of cases of pseudo-mem- 
branous angina in scarlet fever are due to streptococci, although under 
special conditions the proportion of diphtheritic cases may be exception- 
ally large. 
The statistics as to the proportion of cases of pseudo-membranous 
inflammations of the throat not due to the diphtheria bacillus, exclusive 
of scarlatinal cases, occurring in New York and Boston, have already 
been given under the headings “ Proportion of Cases of Suspected Diph- 
theria Proved to be Diphtheria,” and “ Membranous Croup.” From these 
it appears that from about 28 to 40 per cent, of the cases of non-scar- 
latinal pseudo-membranous anginas are pseudo-diphtheria, the percent- 
age in some series being larger and in others smaller. The high per- 
centage of such cases in Park’s first series is altogether exceptional and 
probably due to special circumstances, among which Park mentions par- 
ticularly the prevalence of scarlatina, the relative infrequency of true 
diphtheria, and the season of the year (February and March). Park 
writes that since then he has found the diphtheria bacillus in a series of 
cases in over 80 per cent. 
Several foreign writers have been impressed with the large number 
of American cases of pseudo-membranous angina and laryngitis in which 
diphtheria bacilli were not found, and have expressed some doubt as to 
the accuracy of the results. We attribute the striking differences in the 
reported statistical results of different investigators mainly to the class 
of cases selected for examination. If only typical and characteristic 
cases of diphtheria, be selected, as has been done by some observers, the 
proportion of cases in which the diphtheria bacillus is missed will be 
small, and may be nil. If, however, the less characteristic cases of 
diphtheria, concerning which, in many instances, no one can be sure 
without bacteriological examination whether they are genuine diph- 
theria or not, be included, there may be a relatively large percentage of 20 
WELCH : BACTERIOLOGY OF DIPHTHERIA. 
cases of pseudo-diphtheria. Foreign statistics, based upon the examina- 
tion of cases admitted to the diphtheria wards of hospitals, in which 
cases, therefore, the clinical diagnosis is diphtheria, such as the statistics 
of Baginsky, in Berlin, Martin, in Paris, and Jansen, in Switzerland, 
agree substantially with the New York and Boston statistics. 
Koplik and Park describe with much detail the anatomical and 
clinical characters of the less characteristic diphtheritic and of the pseudo- 
diphtheritic cases. Koplik’s observations as to the former have already 
been cited. In these less characteristic cases neither the location nor 
the character of the diphtheritic inflammations of the throat suffice to 
distinguish positively the true from the false diphtherias, and a positive 
diagnosis must rest upon the bacteriological examination. 
In the great majority of cases which have been examined with suffi- 
cient care, a streptococcus, not differing apparently from the strepto- 
coccus pyogenes or erysipelatis, has been the predominant organism in 
pseudo-diphtheria and is believed to be the cause of this affection. In 
a small number of cases generally, but in Morse’s examinations in a 
large number of cases, staphylococci appear to have been the causative 
micro-organism. In a still smaller group of cases the diplococcus lanceo- 
latus has been assigned as the causative factor. Koplik has met the 
coccus of Roux and Yersin. He also reports four cases of tonsillitis 
without membrane in which the pseudo-diphtheria bacillus was found 
without the typical virulent diphtheria bacillus. 
Park reports the mortality in 408 consecutive cases of pseudo-diphtheria 
bacteriologically examined in New York, and not complicating scarlet 
fever, to have been only 1,7 per cent. Of the seven fatal cases only two 
were over five years of age. The five deaths in young children were 
all in laryngeal cases. He considers that nearly all of the deaths in 
pseudo-diphtheria are due to complications, the most important being 
scarlet fever, membranous laryngitis, and broncho-pneumonia. At the 
same period the mortality from true diphtheria in New York was 27 per 
cent. 
In striking contrast to this low mortality in pseudo-diphtheria is that 
found by Morse in the Boston City Hospital, where 25 per cent, of the 
pseudo-membranous cases without Loeffler bacilli and without scarlet 
fever died. The difference between Park’s and Morse’s results is probably 
to be explained by the fact that Park’s cases Avere largely the usual mild 
ones in private practice, Avhereas Morse’s cases were of sufficient severity 
to be sent to the hospital, many being laryngeal cases, and many dying 
within twenty-four hours after admission, the great majority being .young 
children from crowded and insanitary tenement districts. The mortality 
in true diphtheria uncomplicated Avith scarlet fever Avas in Morse’s cases 
41 per cent. Park also has noted the greater mortality of pseudo-diph- 
theria in the hospital cases as compared with those in private practice. WELCH: BACTERIOLOGY OF DIPHTHERIA. 
21 
As is well known, there is much difference of opinion among physicians 
as to the contagiousness of throat affections due to streptococci and other 
cocci. In order to determine this point, the Health Department of New 
York, as reported by Park, investigated 113 consecutive cases of pseudo- 
diphtheria occurring in 100 families, and at the same time 70 consecutive 
cases of diphtheria in 50 families. A history of contact with another 
case was found in 14 of the 113 cases of pseudo-diphtheria, and in 33 of 
the 70 diphtheria cases. In 9 of the 100 families with pseudo-diphtheria 
there was more than one case, and in 13 of the 50 families with diphtheria 
there was more than one case. It did not seem in an investigation of 
500 cases of pseudo-diphtheria that secondary cases were any less liable 
to occur where the primary case was isolated than where it was not. It 
is considered that where two cases occurred in a family together, or within 
a short period of each other, they may have been due to some common ex- 
posure rather than to direct contagion. Park believes that in the majority 
of cases of pseudo-diphtheria the streptococci concerned are those already 
existing in the healthy throat, and that the presence of certain infectious 
diseases and exposure to cold, dampness, and insanitary surroundings, 
are among the exciting causes. While not denying the possibility of 
contagion, he considers that the degree of communicability is only 
moderate and of minor importance. Even admitting the possibility of 
contagion, he argues that the very slight mortality in uncomplicated 
pseudo-diphtheria justifies the rule of the Health Department in not 
keeping this class of cases under supervision after they have been proved 
bacteriologically not to be true diphtheria. The question of isolation is 
thus left to the discretion of the attending physician. 
That a comparatively small number of cases of membranous croup 
are due to streptococci has already been stated. Woods has reported 
two cases of croupous conjunctivitis following measles, in which strepto- 
cocci, but no Loeffler bacilli, were found. 
Persistence of Diphtheria Bacilli in the Throat during 
and after Convalescence from Diphtheria.—During the ten 
months preceding May, 1894, Park with his co-workers in the Health 
Department of New York has examined 752 cases of diphtheria with 
reference to the length of time the diphtheria bacilli remain in the throat. 
Cultures were made at the beginning of the disease, and again-at short 
intervals after disappearance of the exudate, until the throat was found 
free of diphtheria bacilli. The custom was to make the second culture 
three days after the complete disappearance of the membrane, and then 
to repeat the culture as long as necessary every fourth or fifth day. In 
325 of these 752 cases the diphtheria bacilli disappeared within three 
days after the complete disappearance of the exudate; in 427 cases the 
diphtheria bacilli persisted for a longer time, viz: in 201 cases for 5 to 
7 days; in 84 cases for 12 days; in 69 cases for 15 days; in 57 cases 22 
WELCH : BACTERIOLOGY OF DIPHTHERIA. 
for 3 weeks; in 11 for 4 weeks, and in 5 for 5 weeks. In a case re- 
cently communicated to the writer by Park the bacilli were found 7 
weeks after disappearance of the membrane. 
The virulence of the diphtheria bacilli after recovery is reported by 
Park in 14 cases, the bacilli being obtained at intervals of 10 to 44 days 
after the inception of the disease. Eight guinea-pigs died within 40 
hours, and one in each of the following periods: 60-70 hours, 5 days, 8 
days, 9 days, 11 days, and 14 days. One guinea-pig survived after ex- 
tensive local necrosis. He concludes that the diphtheria bacilli which 
persist in the throat after an attack of diphtheria are always virulent 
for some time. In those exceptional cases in which the bacilli persist 
for a very long time they are found occasionally to lose their virulence 
a few days before their final disappearance, while in other cases they re- 
tain their virulence to the end. In one case the bacilli were virulent 8 
weeks after the onset of the disease and 7 weeks after the disappearance 
of the membrane. That the cases themselves do not seem so liable to 
spread diphtheria is probably largely on account of the relatively small 
number of the bacilli in the convalescent throats, as compared with 
those showing the lesions of diphtheria. Reference has already been 
made to the rule of the Health Department to keep cases of diphtheria 
under supervision until the diphtheria bacilli have disappeared, and to 
practise disinfection as soon as they have vanished from the throat. 
Park reports that thorough irrigation of the throat and nose with 1 to 
4000 bichloride of mercury solution every few hours was attended by 
disappearance of the bacilli within three or four days after disappear- 
ance of the false membrane in from one-half to two-thirds of the cases. 
In the remaining cases the bacilli persisted from four to twenty days, 
notwithstanding the application of the bichloride solution. The dura- 
tion of persistence of the bacilli with irrigation with simple salt-water 
was three days less than with bichloride irrigation. 
Where cultures cannot be made it is recommended to continue the 
isolation of diphtheria patients for at least three weeks after the disap- 
pearance of the membrane: 
Morse investigated twenty-five cases of diphtheria with reference to 
the length of time the diphtheria bacilli persist in the throat and nose. 
He found the average duration of their presence after disappearance of 
the membrane to be ten days, and this to be the same for both throat 
and nose, although they were found longer in the throat in some cases, 
and in the nose in others. The bacilli disappeared in one case the day 
after the throat was clear; in three, three days after, and in one, four 
days after. In two cases in which the bacilli were never found in the 
nose, they remained in the throat ten and seventeen days respectively. 
In other cases they were present: in the throat thirty-seven days, in WELCH: BACTERIOLOGY OF DIPHTHERIA. 
the nose thirty-six days; in the throat twenty-two days, in the nose 
eighteen days; in the throat ten days, in the nose seventeen days; and in 
both twenty-seven days. The bacilli obtained after ten days were found 
of usual virulence; in other cases of this group the virulence is not 
recorded. Patients are not permitted to leave the hospital until the 
diphtheria bacilli have disappeared from both throat and nose. 
Presence of Diphtheria Bacilli in Healthy Throats of 
Persons Exposed to Diphtheria.—An interesting investigation has 
been carried out by Park to test the frequency with which the healthy 
throats of children contain diphtheria bacilli in families where a case 
of diphtheria exists and where little or no isolation is undertaken. The 
throats of fourteen families were investigated, in which there were forty- 
eight children. In 50 per cent, of these virulent diphtheria bacilli were 
found; 40 per cent, developed later, to a greater or less extent, the 
lesions of diphtheria. It is noted in Park’s paper that, in these families, 
the conditions were the best possible for the transmission of the bacilli 
from one to the other. In families where the case of diphtheria was 
well isolated, the bacilli were found in less than 10 per cent, of the 
children. 
The cases, as well as others to be mentioned presently, in which viru- 
lent diphtheria bacilli are found, sometimes in large number, in healthy 
throats of persons who do not develop diphtheria, prove that virulent 
diphtheria bacilli may be present in the throat and multiply there with- 
out causing any visible lesions. As has recently been pointed out with 
much clearness by Escherich, in order to cause diphtheria they must find 
susceptibility to their pathogenic action, which susceptibility may be 
local, or general, or both. 
It is, for several reasons, of practical value to make bacteriological 
examinations of the healthy children’s throats in families where diph- 
theria has developed, or who have been exposed to diphtheria, espe- 
cially where isolation is defective. Experience has shown, as appears 
from Park’s paper, that antiseptic irrigations and cleansing treatment of 
the throat in such cases greatly reduce the liability to develop diphtheria. 
The dissemination of the disease is prevented by isolating in 
whom the diphtheria bacilli are found. Doubtless, not a few cases of 
diphtheria of obscure causation are referable to those who without the 
symptoms and lesions of diphtheria carry about the virulent bacilli. 
Park says : “All members of an infected household should be regarded 
as under suspicion, and in those cases where isolation is not enforced 
the healthy as well as the sick should be prevented from mingling with 
others until cultures or sufficient lapse of time give the presumption 
that they are not carriers of contagion.” 
For interesting illustrative cases and further details on this important 
matter, Park’s paper should be consulted. 24 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
Presence of Diphtheria Bacilli in Healthy Throats where 
No History could be Obtained of Exposure to Diphtheria.— 
Park and Beebe examined the healthy throats of three hundred and thirty 
persons in New York who gave no history of direct contact with diph- 
theria. They found non-virulent, but otherwise characteristic, diphtheria 
bacilli in twenty-four, virulent characteristic diphtheria bacilli in eight, 
and non-virulent pseudo-diphtheria bacilli in twenty-seven. The viru- 
lence was tested by inoculating half-grown guinea-pigs with \ to 1 
per cent, of their weight of forty-eight-hour bouillon cultures grown 
at body temperature. The non-virulent diphtheria bacilli produced acid 
in bouillon, and did not differ morphologically or in cultures from 
virulent diphtheria bacilli. Such bacilli are not regarded by Park as 
pseudo-diphtheria bacilli, but as genuine diphtheria bacilli devoid of 
virulence. The pseudo-diphtheria bacilli usually clouded bouillon and 
did not render it acid, and presented the usual characters of the pseudo- 
diphtheria bacilli to be described subsequently. 
The non-virulent but otherwise characteristic diphtheria bacilli were 
abundant in the primary cultures from seventeen throats, and present 
in small number in the cultures from seven. In only one guinea-pig 
was there appreciable reaction after inoculation. Two hundred and 
eighty of the cases from which the cultures were made were children 
under twelve years of age (bacilli in twenty-two cases), while fifty were 
adults (bacilli in two). The non-virulent diphtheria bacilli persisted in 
four of the throats for four weeks, in one for three weeks, and in three 
for two weeks. 
Of the eight cases in which virulent diphtheria bacilli were found, 
five were children in an asylum where from time to time cases of true 
diphtheria had occurred. Of the remaining three, one was from a house 
where a case of supposed croup had existed three weeks before. Two 
of the eight children developed diphtheria some days after making 
the cultures. The other six never developed any symptoms of diph- 
theria. The guinea-pigs inoculated with the cultures died in from 
twenty-eight to forty hours. 
Fro$n the groups of cases studied under this and the preceding head- 
ings Park concludes that virulent diphtheria bacilli are present in 
probably about 1 per cent, of the healthy throats in New York City. 
Most of the persons in whose throats they exist have been in direct 
contact with cases of diphtheria. Many of those whose throats contain 
the virulent bacilli never develop diphtheria. 
Occurrence of Diphtheria Bacilli Outside of the Human 
Body.—In his first paper Park says that cultures made from the dried 
stains on spreads, pillow-cases, and sheets, where soiled by the expectora- 
tion of diphtheria patients, showed in every case a few colonies, at least, 
of the Loefiler bacillus. The sputum of patients, though apparently WELCH : BACTERIOLOGY OF DIPHTHERIA. 
25 
free from bits of membrane, usually contained the bacilli in large 
number. 
Important results have been obtained by Wright and Emerson, who 
have kindly furnished the writer an abstract of their unpublished work 
so far as it has yet been carried. They made cultures on blood-serum 
from the clothing, shoes, hair, and finger-nails of nurses in attendance 
on diphtheria patients, and also from the dust and various objects within 
the diphtheria ward of the Boston City Hospital. This ward contains 
seventy beds, which are generally nearly all occupied. The hygienic 
condition of the ward is stated to be good. Material, such as dust, etc., 
was collected for the most part on a sterilized platinum wire and applied 
to the surface of the culture medium. About twenty cultures in all 
have been made, of which five yielded Loeffler bacilli in small numbers. 
In all of the positive cases the bacilli isolated in pure culture were 
tested thoroughly as to their virulence and their morphological and 
cultural characters, and positively identified. In the latter respect all 
were characteristic diphtheria bacilli. It may be especially noted that 
all rendered bouillon acid within forty-eight hours. In two of the five 
cases the bacilli were of usual virulence, in two they were weakened in 
virulence, although killing guinea-pigs, and in one they caused only 
local reaction from which the animal recovered. The virulence was 
tested by inoculating guinea-pigs subcutaneously with i to 1 per cent, 
of their weight of twenty-four- to forty-eight-hour bouillon cultures. 
From eight inoculated guinea-pigs which died, the characteristic bacilli 
were recovered in each instance, even when death occurred after some 
weeks. 
The Loeffler bacilli were found on three shoes, each belonging to a 
different nurse, once on the hair of a nurse, the culture being taken from 
the hair above the ear, and once on a brush used in sweeping the floor 
of the ward. 
The weakening of the virulence in two cases (in one case the guinea-pig 
died after seven and one-half days, and in another after some weeks, 
bacilli from each being recovered from the seat of inoculation) and the 
production of only slight local reaction from which the animal recovered 
in the case in which the bacilli were found on the hair of a nurse, sug- 
gest attenuation of virulence by unfavorable environment. 
These suggestive observations of Wright and Emerson tell their own 
story and need no special comment. 
No observations have been reported in this country of diphtheria as a 
spontaneous affection of domestic animals. Abbott was unable to con- 
firm Klein’s observations of the elimination of diphtheria bacilli through 
the milk of cows inoculated with virulent cultures of the Loeffler bacillus. 
Methods of Dissemination of Diphtheria.—How manifold 
may be the modes of conveyance of the diphtheria bacillus, and howr 26 
WELCH: BACTERIOLOGY OF DIPHTHERIA. 
obscure and difficult or even impossible to trace may be the origin of 
some cases of diphtheria, is evident from observations which have been 
mentioned. Park from his rich experience summarizes and illustrates 
with interesting examples some of the ways in which the diphtheria germ 
may be transported. 
Here we cannot do more than enumerate some of the sources of infec- 
tion which have been established by bacteriological investigations, to 
wit: the pseudo-membranes, exudates and discharges of diphtheria 
patients, both those with typical diphtheria and those with mild and 
little characteristic forms of the disease; infected clothing, bedding, 
and other objects ; occupying rooms where diphtheria has existed; con- 
valescent or recovered cases in whom the diphtheria bacilli persist; per- 
sons who have been in contact with others having diphtheria bacilli on 
their persons or clothing, or with infected objects, such persons sometimes 
carrying diphtheria bacilli in their throats for days or weeks without 
lesion. The investigations of Wright and Emerson show on what 
varied objects the diphtheria bacilli may be carried. Park traced one 
group of cases of diphtheria to a candy-store kept by a family in 
which occurred a case of diphtheria. Children who bought candy at 
this store acquired diphtheria, and other children who came in contact 
at school with the healthy children of this family also developed diph- 
theria. 
The investigations of the Health Department indicate that at present 
the whole tenement-house district of New York is an infected area. In 
plotting out on a map the distribution of cases of diphtheria in New 
York it was interesting to note two types of epidemics, one essentially of 
neighborhood infection, the other in which the cases could be attributed 
to infection at school. It was observed that a whole school district would 
suddenly become the seat of scattered cases. At times, in a certain area 
of the city from which several schools drew their scholars, all the cases 
of diphtheria would occur in families whose children attended one school, 
the children from the other schools being for a time exempt. 
In about one-half of the cases of diphtheria in New York careful 
inquiry failed to show connection with other cases. 
Influences which increase susceptibility to diphtheria doubtless play a 
role in determining the development of the disease. The majority of 
adults and many children are insusceptible. What these predisposing 
influences are we do not know, save the influence of age. That special 
local conditions, the presence of throat affections and the association 
of the diphtheria bacillus with other micro-organisms, particularly 
streptococci, are predisposing factors seems highly probable. It is 
also probable that the degree of virulence of the diphtheria bacillus 
and the number of bacilli received into the body must be taken into 
account. WELCH; BACTERIOLOGY OF DIPHTHERIA. 
We possess no evidence that the diphtheria bacillus finds a natural 
home outside of the human body, although it may survive for months 
on objects outside of the body. Park found living diphtheria bacilli on 
bits of membrane dried for seventeen weeks, and in blood-serum cultures 
seven months old. 
Pseudo diphtheria Bacillus.—The various questions relating to 
the pseudo-diphtheria bacillus have been investigated by Abbott, 
Koplik, and Park. 
In fifty-three cases of various throat affections, mostly without suspicion 
of diphtheria, examined bacteriologically by Abbott, he found in three 
bacilli indistinguishable morphologically or in cultures from the Loeffler 
bacillus, but entirely devoid of virulence, as tested repeatedly on guinea- 
pigs. One of the cases was suspicious of diphtheria, there being a grayish 
membrane on the tonsils; one was a case of syphilitic pharyngitis with- 
out membrane, and the other was follicular tonsillitis. From a fourth 
case of this series with a grayish-white deposit on the tonsils, Abbott 
cultivated a bacillus resembling the Loeffler bacillus, but somewhat 
thicker, growing more luxuriantly on agar, clouding bouillon and grow- 
ing visibly on potato, exceptionally invisibly. This bacillus was wholly 
non-pathogenic for guinea-pigs. As already mentioned, Abbott and his 
pupil, Ravenel, have found in two cases of membranous rhinitis bacilli 
indistinguishable from the Loeffler bacillus except that they failed to 
kill guinea-pigs, although producing local reaction. 
Abbott’s conclusion is that the diphtheria bacillus varies in its viru- 
lence and that non-virulent varieties of the bacillus occur. He says 
that the name pseudo-diphtheria bacillus should not be applied to those 
bacilli which possess all of the morphological and cultural characters of 
the Loeffler bacillus and are devoid of virulence. These are simply non- 
virulent diphtheria bacilli. He reserves the term pseudo-diphtheritic 
bacillus “ for that organism or group of organisms (for there are prob- 
ably several) that is enough like the diphtheria bacillus to attract 
attention, but is distinguishable from it by certain morphological and 
cultural peculiarities aside from the question of virulence.” 
Koplik does not seem to have met with a bacillus presenting all the 
morphological and cultural properties of the virulent diphtheria bacillus 
but devoid of virulence. He emphasizes the importance, in testing viru- 
lence, of observing the precautions especially signalized by Behring and 
by Escherich, as already mentioned, and gives examples showing that 
mistakes on this point can readily be made where old cultures and insuf- 
ficient doses are used. Koplik has, however, in six cases out of a large 
number examined found the pseudo-diphtheria bacillus essentially as 
described by Hoffmann, and he would limit the name pseudo-diphtheria 
bacillus to the bacillus presenting these definite characters. This pseudo- 
diphtheria bacillus he describes in his first article as shorter and slightly 28 
welch: bacteriology of diphtheria. 
plumper than the real bacillus, but subsequently he describes it as an exact 
counterpart of the Loeffler bacillus in shape, size, and staining peculiarities, 
with the exception of deeper staining with methylene-blue. Actual meas- 
urements do not show any constant difference in thickness or length from 
the Loeffler bacillus. It grows upon blood-serum, potato, and gelatin, like 
the genuine bacillus. Upon agar the growth is always more luxuriant, 
thicker and whiter than that of the real bacillus. In alkaline peptone 
bouillon the pseudo-bacillus causes in twenty-four hours diffuse clouding 
with abundant deposit. The reaction remains distinctly alkaline. 
Koplik communicates to the writer an unpublished observation to the 
effect that if the pseudo-bacillus be cultivated in closed tubes of Pasteur 
pattern, from which the oxygen has been absorbed by pyrogallate of 
potassium, there is an abundant sediment with diffuse clouding of the 
bouillon, and in forty-eight hours the reaction is found to be acid. 
Neither aerobic nor the acid anaerobic cultures are lethal to guinea- 
pigs, even in enormous doses. Nor does the preparation of an animal 
for weeks by the injection of such repeated doses protect it from the 
effects of small doses of a fresh culture of the virulent bacillus. This 
was proved not only upon guinea-pigs, but also upon sheep and dogs. 
Koplik’s first article is illustrated with beautiful photographs of the real 
and the false diphtheria bacilli in microscopical specimens and in cul- 
tures. It contains also a very satisfactory photograph of involution 
forms of the diphtheria bacillus. 
The pseudo-bacillus was found by Koplik in four cases, already men- 
tioned, with inflammation of the tonsils, without the real bacillus. In 
two cases of lacunar tonsillar diphtheria virulent typical diphtheria 
bacilli persisted in the crypts, in one case for three weeks, and in the 
other case for two weeks. At the end of these periods the virulent 
bacillus gave place to a non-virulent bacillus indistinguishable morpho- 
logically from the real bacillus, but presenting the cultural characters 
above described of the pseudo-bacillus, this bacillus being found abund- 
antly in exactly the same situations in which the virulent bacillus pre- 
viously existed. These non-virulent bacilli persisted in the tonsillar 
lacunae up to the sixth week after the onset of the illness in one case. 
Koplik suggests the possibility that under the influence of the lymph 
and leucocytes of the tonsils, the virulent bacillus was transformed into 
the non-virulent form. He considers, however, the relationship be- 
tween these two bacilli to be still an open question, but upon the whole 
he seems to be of the opinion that they are distinct species. When 
found, the pseudo-diphtheria bacilli were abundant in the cultures. 
Koplik’s results may be said to be confirmatory of those of Escherich. 
Park found, in 20 cases diagnosticated as diphtheria, the bacilli to be 
virulent in all, but in three of these cases the cultures from the first 
colony selected, although characteristic, were not virulent, while, from WELCH: BACTERIOLOGY OF DIPHTHERIA. 
29 
other colonies in the same cases they were fully so. As already stated, 
Park used in testing virulence forty eight hours’ broth cultures injected in 
doses of one-quarter to one-half or even one per cent, of the body-weight 
of the guinea-pig—selecting, where possible, young guinea-pigs. Park, 
therefore, confirms the observation of Roux and Yersin as to the pos- 
sible coexistence of virulent and non-virulent bacilli in the same throat. 
He considers that in suspicious cases one should not be content with 
cultures from a single colony, if this should prove not to be virulent. 
In this connection it may be mentioned that Park found no definite 
relation between the virulence of the cultures and the severity of the 
case. Nor was he able in an extended research to discover a relation- 
ship between the size of the bacillus and its virulence such as has been 
claimed by some investigators. He states that the results of 1613 cul- 
tures in which this factor was carefully noted in relation to the severity 
of the case indicate that in New York the great majority of cases of 
diphtheria yield in cultures bacilli of medium size which are charac- 
teristic in shape and in manner of staining, and that in a moderate 
number the bacilli are much longer, and in about an equal number they 
are much shorter. Both clinical histories and animal experiments 
showed that as long as in shape and staining the bacilli are charac- 
teristic, nothing as regards their virulence can be judged from their 
size. Those bacilli, on the other hand, which are short and stain uni- 
formly with methylene-blue usually turn out to be of the pseudo- 
diphtheria type which have no virulence in animals. 
It has already been mentioned that Park found exceptionally in cases 
in which diphtheria bacilli persisted in the throat a long time after 
recovery from diphtheria, attenuation of virulence to a point in which 
the cultures, although producing local reaction, failed to kill guinea-pigs. 
We have cited already the investigations of Park and Beebe upon the 
healthy throats of 330 persons who gave no history of direct contact 
with diphtheria. In 24 of these they found bacilli indistinguishable from 
the diphtheria bacillus except by absence of virulence, which was tested 
by injecting forty-eight-hour broth cultures in doses of one-half to one per 
cent, of their weight into half-grown guinea-pigs. In 19 of these 24 
cases the bacilli were grown in broth. In all of these the bacilli formed 
acid by their growth in forty-eight hours, sometimes more, sometimes less 
acid than control cultures of virulent bacilli. In 13 the broth culture 
was entirely characteristic, like that of the virulent bacillus, while in 6 
the culture became more or less clouded, an effect which is exceptionally 
produced also by the virulent bacillus. No difference was found as to 
the growth on blood-serum. Upon agar the growth was typical of that 
of the virulent bacillus in 11 cases, while from 7 the bacilli grew in a 
less typical manner, but always in ways seen occasionally with the virulent 
form. Of the guinea-pigs inoculated with cultures from 15 of the cases, 30 
WELCH : BACTERIOLOGY OF DIPHTHERIA. 
in only one was there any appreciable local reaction, and this subsided 
within four days. A very slight degree of immunity seemed to be 
afforded to some of the guinea-pigs by the injection. 
In 27 cases the pseudo-diphtheria bacillus, which, as well as the genuine 
diphtheria bacillus, has been most satisfactorily photographed in cover- 
slip specimens and cultures by Park, was found presenting in general 
the characters described above. Park describes this bacillus as shorter 
and thicker and more uniform in size and staining than the virulent 
Loefller bacillus. It clouded and formed alkali in bouillon in the first 
forty-eight hours, grew more luxuriantly on agar, and was not patho- 
genic. Park would confine the name pseudo-diphtheria bacillus to the 
bacillus or group of bacilli presenting these general characters. 
Park, as well as Abbott, therefore, recognizes a non-virulent form of the 
diphtheria bacillus, and contends that bacilli indistinguishable from the 
diphtheria bacillus except by absence of virulence, should not be called 
pseudo-diphtheritic. He admits certain morphological and cultural 
variations of the true diphtheria bacillus, such as variations in size, 
occasional clouding of bouillon, exceptional luxuriance of growth on 
serum and agar, etc., but the production of acid in bouillon he regards 
as essential to the diagnosis of the diphtheria bacillus. 
The pseudo-diphtheria bacillus, as defined above, is regarded by Park 
as a species distinct from the genuine diphtheria bacillus, either in its 
virulent or its non-virulent state. Park calls attention to the confusion 
introduced into the discussions on the pseudo-diphtheria bacillus by the 
fact that some have given this name to bacilli indistinguishable from the 
diphtheria bacillus except by absence of virulence, whereas others have 
worked with the genuine pseudo-diphtheria bacillus, which presents cul- 
tural and morphological differences from the genuine diphtheria bacillus. 
It would seem to be established, therefore, by the investigations of 
Abbott and Park, that a bacillus in no way distinguishable from the 
diphtheria bacillus except by absence of virulence exists. Although 
other investigators have included this non-virulent but otherwise char- 
acteristic diphtheria bacillus under the designation pseudo-diphtheria 
bacillus, they contend that this name is inappropriate for this bacillus, 
which should be considered as the genuine diphtheria bacillus, which may 
present all degrees of virulence down to complete harmlessness, as tested 
on guinea-pigs. This non-virulent bacillus has been found only in a 
comparatively small number of cases, these cases being chiefly without 
characteristic lesions of diphtheria. Occasionally the virulent and the 
non-virulent diphtheria bacilli are found side by side in diphtheria, and 
occasionally the virulent bacillus has given place to the non-virulent 
bacillus during or after recovery from diphtheria. 
Abbott, Koplik, and Park would limit the name pseudo-diphtheria 
bacillus to bacilli which, although bearing resemblance to the diphtheria WELCH : BACTERIOLOGY OF DIPHTHERIA. 
31 
bacillus, differ from it not only by absence of virulence toward guinea- 
pigs but also by cultural characteristics. 
Abbott considers that there is a group of bacteria which in this sense 
may be called pseudo-diphtheritic, and that they are distinct species from 
the diphtheria bacillus. Koplik describes with much detail a special 
bacillus observed by him in six cases, which he considers to be identical 
with the original pseudo-diphtheria bacillus of Hoffmann, and to which 
he would limit the name pseudo-diphtheria bacillus. This bacillus 
grows on agar more luxuriantly than the genuine diphtheria bacillus, 
and it does not change the reaction of alkaline glucose bouillon in 
aerobic cultures, although it produces acid in anaerobic cultures. While 
not expressing a positive decision, he seems inclined to regard this bacil- 
lus as distinct in species from the genuine diphtheria bacillus. 
Park has probably worked with the same bacillus, at least the same as 
the one described by Koplik in his first article, and he also would limit the 
name pseudo-diphtheria bacillus to this bacillus, or to a group of bacilli 
presenting these several characteristics, if, as is probable, such a group 
exists. He considers that this bacillus, or these bacilli, differ from the 
genuine diphtheria bacillus at least as much as the colon bacillus differs 
from the typhoid bacillus. The pseudo-diphtheria bacillus was found in 
only a small number of cases out of the many examined, and appeared 
to have nothing to do with diphtheria. 
Summary.—This paper is a report of the results of the bacteriological 
study of diphtheria in the United States up to May, 1894, so far as these 
results are of interest for the purposes of this Congress. The investigations 
were made by various men in New York, Baltimore, Boston, and 
Philadephia. 
Some of the more important conclusions may be summarized as 
follows: 
1. The Health Department of New York has undertaken the bac- 
teriological examination of all cases of suspected diphtheria in that city, 
unless objection is made by the attending physician or unless it is not 
deemed advisable to disturb the patient by such examination. The 
methods employed are described in detail. During the year ending 
May 4, 1894, cultures were made from 5611 cases of suspected diph- 
theria. The results have proven satisfactory, and are utilized not only 
for diagnosis, but also to control the supervision and isolation of the 
cases. 
2. Of 6156 cases of suspected diphtheria in New York and Boston, 
per cent, were proven bacteriologically to be true diphtheria—or, if 
we include only those cases in which the bacteriological examination 
was considered to be entirely satisfactory—of 5340 cases, 67i per cent, 
were true diphtheria. These were pseudo-membranous inflammations 32 
welch; bacteriology of diphtheria. 
of the throat and air-passages uncomplicated for the most part with 
scarlet fever. 
3. At least 80 per cent, of the cases of membranous croup in New 
York were diphtheria, and only 14 per cent, were shown not to be 
diphtheria. 
4. Fifteen cases of fibrinous rhinitis and 4 cases of primary and 
exclusively nasal diphtheria were all due to the diphtheria bacillus. 
5. Various forms of atypical diphtheria, many without membrane, 
and with the characters of simple catarrhal angina and follicular 
tonsillitis, are described. 
6. Instances of unusual localizations of the diphtheria bacillus, as in 
the middle ear, in wounds, ulcers, abscesses, conjunctivse, lungs, heart- 
valves, and the distribution of the bacilli at autopsies of human beings 
and of guinea-pigs dead of diphtheria, are described. 
7. The various bacteria found associated with the diphtheria bacillus, 
the most important pathogenic forms being streptococci, staphylococci, 
and the diplococcus lanceolatus, are considered. 
8. In general the great majority of cases of pseudo-membranous 
anginas in scarlet fever are due to streptococci, but where diphtheria is 
prevalent and opportunities are favorable for exposure to diphtheria a 
large proportion may be due to the diphtheria bacillus. The statistics in 
Baltimore and in Boston present interesting contrasts in illustration of 
this point. Four cases of diphtheria complicating typhoid fever are 
described. 
9. The name pseudo-diphtheria is applied to pseudo-membranous 
inflammations of the throat and air-passages not caused by the diph- 
theria bacillus. The most important and common micro-organism in 
pseudo-diphtheria is the streptococcus pyogenes, but other bacteria may 
be the cause. The mortality in these affections is low in private prac- 
tice, being 1.7 per cent, in 408 consecutive cases in New York. In 
hospitals it may be as high as 25 per cent. Death is generally due to 
some complication, the most important complications being scarlet fever, 
membranous laryngitis, and broncho-pneumonia. The disease seems to 
be only slightly, if at all, contagious. For this reason, and on account 
of the low mortality in uncomplicated cases, those cases which are 
proved bacteriologically not to be true diphtheria are not kept under 
supervision by the Health Department in New York. Until such proof 
suspicious cases are treated as diphtheria. 
10. Of 752 cases of diphtheria in New York, the diphtheria bacilli 
in 325 disappeared within three days after the complete disappearance 
of the exudate. In 427 cases the bacilli persisted for a longer time, 
viz., in 201, for from five to seven days; in 84, for twelve days; in 69, for 
fifteen days; in 57, for three weeks; in 11, for four weeks; and in 5, for 
five weeks. In one case, virulent bacilli were found seven weeks after WELCH: BACTERIOLOGY OF DIPHTHERIA. 
33 
disappearance of the exudate. The cases are kept under supervision 
until the bacilli have disappeared. Sometimes they disappear first from 
the nose; at other times, first from the throat. 
11. In fourteen families, with forty-eight children, where little or no 
isolation of a case of diphtheria in each family was undertaken, virulent 
diphtheria bacilli were found in 50 per cent, of the children, of whom 
40 per cent, later developed diphtheria. The bacilli were found in less 
than 10 per cent, of the children in families where the case of diphtheria 
was well isolated. 
Antiseptic irrigation and cleansing treatment of the throat lessens the 
liability of those thus exposed to develop diphtheria. 
All members of an infected household should be regarded as under 
suspicion, and where isolation is not enforced the healthy as well as the 
sick should be prevented from mingling with others until cultures or 
sufficient lapse of time give the presumption that they are not carriers 
of contagion. 
12. Diphtheria bacilli may be present and multiply in the throat 
without causing symptoms or lesions. They must find susceptibility to 
their pathogenic action in order to cause diphtheria. 
13. In three hundred and thirty persons who gave no history of direct 
contact with diphtheria, virulent diphtheria bacilli were found in eight, 
of whom only two subsequently developed diphtheria. Bacilli, indis- 
tinguishable morphologically or in cultures from the diphtheria bacillus, 
including the formation of acid in forty-eight hours in bouillon, but 
entirely devoid of virulence, were found in twenty-four of these persons, 
in most of these instances in large numbers. The pseudo-diphtheria 
bacillus was found in twenty-seven. 
14. Instances are given in which the diphtheria bacilli were found on 
various objects outside of the human body, viz., bed-clothing soiled 
with discharges of diphtheria patients; the shoes and the hair of nurses 
in attendance on diphtheria patients, and a brush used in sweeping the 
floor of a diphtheria ward. 
15. Some of the various ways in which the diphtheria germ is trans- 
ported are summarized. 
16. A bacillus in no way distinguishable in morphology or in cul- 
tures, including the formation of acid in bouillon, from the usual 
diphtheria bacillus, but devoid of virulence, exists. The virulence was 
tested by injecting into half-grown guinea-pigs i to 1 per cent, of their 
weight of forty-eight-hour bouillon cultures. This bacillus, although it 
has been called by some investigators the pseudo-diphtheria bacillus, 
should not be so designated. It is the genuine diphtheria bacillus devoid 
of virulence. It was met with in a comparatively small number of cases 
out of a large number examined. Exceptionally, it may occur together 
with the virulent diphtheria bacillus in diphtheria, and occasionally it 34 
WELCH : BACTERIOLOGY OF DIPHTHERIA. 
takes the place of the virulent bacillus during or after recovery from 
diphtheria. In several instances it was found in healthy throats. 
The name pseudo-diphtheria bacillus should be confined to bacilli 
which, although resembling the diphtheria bacillus, differ from it not 
only by absence of virulence, but also by cultural peculiarities, the most 
important of the latter being greater luxuriance of growth on agar and 
the preservation of the alkaline reaction of bouillon cultures. The 
pseudo-diphtheria bacillus may render bouillon cultures acid in forty- 
eight hours when grown anaerobically. The pseudo-diphtheria bacillus 
in this sense was found in a number of cases, but not frequently. It is 
probably of different species from the genuine diphtheria bacillus, and 
is without diagnostic importance. 
Articles cited in the Text. 
Abbott, A. C.: The Relation of the Pseudo-Diphtheritic Bacillus to the Diphtheritic Bacillus. 
Bulletin of the Johns Hopkins Hospital, August, 1891. 
Further Studies upon the Relation of the Pseudo-Diphtheritic Bacillus to the Diph- 
theritic Bacillus. Bulletin of the Johns Hopkins Hospital, Octoher-Novemher, 1891. 
The Etiology of Membranous Rhinitis (Rhinitis Fibrinosa). The Medical News, May 
13,1893. 
The Results of Inoculations of Milch Cows with Cultures of the Bacillus Diphtherias. 
The Journal of Pathology and Bacteriology, October, 1893. 
and Ohriskey, A. A.: A Contribution to the Pathology of Experimental Diphtheria. 
Bulletin of the Johns Hopkins Hospital, April, 1893. 
Booker, William D.: The Relation of Pseudo-Diphtheritic Angina to Diphtheria, with special 
reference to Scarlatinal Pseudo-Membranous Angina. Bulletin of the Johns Hopkins Hospital, 
October-November, 1892. 
As to the Etiology of Primary Pseudo-Membranous Inflammation of the Larynx and 
Trachea, with Remarks on the Distribution of the Diphtheria Bacilli in Organs of the Body 
Distant from the Seat of Local Infection. Transactions of the American Pediatric Society, 
vol. v. 
Councilman, W. T.; The Pathology and Diagnosis of Diphtheria. The American Journal 
of the Medical Sciences, November, 1893. 
Flexner, Simon: Diphtheria with Broncho-Pneumonia. Bulletin of the Johns Hopkins 
Hospital, April, 1893. 
Howard, W. T., Jr.; Acute Ulcerative Endocarditis due to the Bacillus Diphtherias. Bulletin 
of the Johns Hopkins Hospital, April, 1893. 
Johnston, Wyatt: A New Method for the Culture of Diphtheria Bacilli in Hard-boiled Eggs. 
The Medical News, December 10, 1892. 
Koplik, Henry ; Forms of True Diphtheria which Simulate Simple Catarrhal Angina. The 
New York Medical Journal, August 27, 1892. 
Acute Lacunar Diphtheria of the Tonsils, with Studies on the Relation of the Real to 
the Pseudo-Bacillus Diphtheriae. The New York Medical Journal, March 10,1894. 
Morse, John Lovett: A Bacteriological Study of Four Hundred Cases of Inflammation of the 
Throat, occurring in Diphtheria and Scarlet Fever, with Especial Reference to Pathogenesis. 
The Boston Medical and Surgical Journal, February 15 and 22, 1894. 
Park, William Halleck: Diphtheria and Allied Pseudo-membranous Inflammations. A 
Clinical and Bacteriological Study. The Medical Record (New York), July 30 and August 6, 
J.892. 
Diphtheria and other Pseudo-membranous Inflammations. A Clinical and Bacterio- 
logical Study. Second Paper. The Medical Record, February 11,1893. 
The unpublished manuscript of a report to the Board of Health of New York contains 
a large part of the observations of Park cited in the text. The examinations for bacteriological 
diagnosis in suspected cases of diphtheria reported in this paper were made by Dr. Park in 
about two-thirds of the cases and by Mr. Alfred Beebe in about one-third. This manuscript, 
which was prepared in part for this report to the Congress, has been kindly placed at the dis- 
posal of the writer. welch: bacteriology of diphtheria. 
35 
Prudden, T. Mitchell: On the Etiology of Diphtheria. An Experimental Study. Amer. Joukn. 
of the Medical Sciences, April and May, 1889. 
Studies on the Etiology of Diphtheria. Second series. The Medical Record, April 18, 
1891. 
Ravenel, M. P.: Notes on Two Cases of Membranous Rhinitis (unpublished manuscript). 
Townsend, Charles W.: Primary Nasal Diphtheria. The Boston Medical and Surgical Jour- 
nal, May 24, 1894. 
Welch, William H.: The Causation of Diphtheria. Transactions of the Medical and Chirur- 
gical Faculty of Maryland, 1891. 
and Abbott, A. C.: The Etiology of Diphtheria. Bulletin of the Johns Hopkins Hos- 
pital, February and March, 1891. 
and Meaner, Simon: The Histological Changes in Experimental Diphtheria. Bulletin 
of the Johns Hopkins Hospital, August, 1891. 
The Histological Lesions Produced by the Toxalbumin ol Diphtheria. Bulletin of the 
Johns Hopkins Hospital, March, 1892. 
TFoods, Hiram: Diphtheritic Conjunctivitis: Report of Two Cases, with the Bacteriologic 
Study of the False Membrane. The Medical News, August 20,1892. 
Wright, J. H.: Manuscript of unpublished work on Diphtheria sent to the writer of this 
report. 
and Emerson, H. C.: On the Occurrence of the Bacillus Diphtherias outside of the 
Body (unpublished manuscript prepared for this report). T*7e Johrijal 
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