MODERN DIFFICULTIES IN 
BACTERIOLOGICAL DIAGNOSIS. 
BY 
J. Gr. ADAMI, M.D., 
Professor of Pathology in the McGill University, Montreal. 
(Reprinted front the Montreal Medical Journal, November, 1894.) MODERN DIFFICULTIES IN BACTERIOLOGICAL 
DIAGNOSIS* 
By J. G. Adami, M.A., M.D., M.E.C.S., 
Professor of Pathology in McGill University, Montreal. 
At a time when in the popular estimation bacteriology 
is showing itself to be of greater and ever greater import 
not only in matters of health and disease, but also in 
the very commonest commercial relations of every-day life, 
and when the world in general seems to be becoming 
rapidly convinced that the microbe is at the bottom of 
everything ; when, in fact, bacteriology has already made 
an ample apology for its existence, it is, I think, well that 
occasionally one of us, not from a sceptical spirit, but 
because of the very strength of his belief in the importance 
of his science, more especially in its relationship to public 
health, should pause, and should, as a bacteriologist, point 
out that matters are not quite so settled, that in fact 
everything is not quite so surely established as in the 
opinion of very many it would seem to be. 
Taking into account the extraordinarily large accumula- 
tion of facts that we now have concerning the bacteria, it is 
wonderful to think that to all intents and purposes the 
advance of bacteriology has been synchronous with the 
* A communication presented to the Montreal meeting of the American Public 
Health Association, September. 1894. 4 
scientific lifetime of so young- a man as I am. There is 
scarce one present here but can remember the days of ample 
doubt as to the pathogenic properties of any of the 
bacteria ; scarce one but can remember the time when 
Pasteur’s wonderful series of observations upon anthrax 
and the bacillus of anthrax hardly received credence. 
From that period one saw passing days of gradually 
lessening doubt, until Koch’s wonderful investigations into 
the bacillus of tuberculosis made men rush to the other 
extreme, made them absolutely sure that whether the 
microbe was discovered or no, specific microbe exists for 
every febrile disease, and for a great number of non-febrile 
diseases. Now, at the present time, there is among bac- 
teriologists, among those deeply read and acquainted with 
the subject, as it were a backward swing of the pendulum, 
to a certain extent. What I mean is that, largely through 
the teaching of the German school of bacteriologists we 
had, but a few years ago, come to look upon every disease 
in which a definite microbe had been discovered, as being 
due to the presence within the organism of some microbe 
whose characteristics were absolutely sharply-defined. 
There was, for example, an absolutely specific microbe of 
cholera, possessing constant properties, constant peculiari- 
ties of growth on various media and constant chemical 
reactions of part of its products, with constant development 
of special ferments. There was a sharply-defined diplo- 
coccus of pneumonia, a bacillus of typhoid that could not 
be confounded with any other microbe. And so on with 
regard to all the important diseases whose germ has been 
discovered. 
Well, I do not wish now to say that this is false ; all that I 
wish to do in this short paper is to impress unon you the ad- 
visability of crying “ Halt ” before we unreservedly stand 
to this belief, and it is of especial importance to the 
members of this Association that the advisability of de- 
liberating long and carefully should be kept in mind ; 
inasmuch as it is just in relation to some of the most wide 5 
spread and epidemical microbes that we have at the present 
moment the greatest difficulty in regard to the exact bac- 
teriological diagnosis. That these microbes, by their 
presence and growth in the system, causes disease no 
sane [and competent bacteriologist has the smallest doubt, 
but we have before us in relation to typhoid, cholera and 
diphtheria, not to mention other cases, a series of problems 
that are as yet unsettled. The right solution of these 
problems is, from the point of view of the public health 
officer, of vital importance. As yet I cannot regard these 
problems as having been fully solved or nearly solved ; 
and in this view I believe I shall have the support of my 
fellow-bacteriologists. 
The main problem before us at the present time is in 
relation to the determination of species. Are we to con- 
clude that there are, it may be, several closely allied species 
which are capable of inducing the main symptoms of any 
given disease, or are we to regard the several slightly diver- 
gent forms which may be gained from different cases of 
what clinically we recognize as a single disease as but 
varieties or races of one species which have obtained more 
or less permanent characters setting them off’ from the type ? 
What, in short, are we to regard as the limits of variability ? 
Apart from a constant recurrence to experimental inocula- 
tion (which is not always possible) how are we surely to 
recognize the pathogenic nature of the form we isolate from 
cases of disease ? 
Take, for instance, what is found in connection with 
typhoid ; no one in our days, who has made actual observa- 
tions, has the slightest doubt as to the cause of that disease ; 
every one is agreed that it is due to a bacillus, having, on 
the whole, well defined characters, if once we obtain the 
baccillus from the body of a patient in a fairly early stage 
of the disease. No one, again, doubts but that typhoid 
spreads through the water, through contamination of the 
water supply, but now here is the difficulty. If we examine? 
in the first place, the water supply supposed to be con- 
taminated, in case after case we may be successful in 6 
discovering on suitable media of growth colonies, or 
growths, which closely correspond to typhoid bacilli ; or, 
again, if we examine the stools of the patient supposed to be 
affected by the disease, there again we may, among crowds 
of colonies presenting but a slight divergence from the 
characters usually regarded as typical of the bacillus of 
enteric fever, find some few colonies only distinguishable 
by the most delicate tests, but still not quite conforming to 
the type, and the question is, are those colonies truly those 
of the typhoid bacillus, or do they represent some closely 
allied species ? For myself I scarcely see how it is possible 
to give a positive answer in either of these cases. It is 
true that in other diseases the point can be settled by 
experimental inoculation into animals ; in enteric fever, 
however, unless one is successful in gaining cultures of the 
microbe direct from the human organism from a typical 
case of the disease and employing them while they are still 
young, inoculation into animals is of no effect. Then there 
is another side to the question. Suppose that one repeats 
the series of experiments made by Babes, and carefully 
examines the peculiarities of the growths obtained from 
different cases of undoubted typhoid at different periods of 
the disease, then it is possible by these means to separate 
out quite a large number of cultures, whose general pro- 
perties, it is true, correspond with those of the typical 
Bacillus Typhi of the text-books, but which at the same 
time in minuter characters differ from the type and from 
each other to quite the same extent as do the cultures of 
doubtful import found in supposed contaminated water and 
in the faeces of suspected cases. Ido not mean to say here 
that in the majority of cases of typhoid one comes across any 
marked divergences from the typo, but in a large number 
of doubtful cases it is that one is most likely to have, and that 
one most frequently does have these slight cultural diver- 
gences, and the question is what is the conclusion at which 
we are to arrive. Are we dealing with varieties of the 
bacillus of typhoid, or are these wholly different and non- 
pathogenic species ? What is to be our diagnosis ? 7 
Or, take again cholera ? Every one, I suppose, is 
acquainted with Cunningham’s remarkable declaration that 
out of sixteen cases of cholera at Calcutta, the home of 
the disease, he was able to isolate no less than ten different 
spirilla resembling each other on the whole, but nevertheless 
in his belief presenting such clear and constant distinc- 
tions that he classed them not as varieties but as species.* 
Thanks to Professor Welch, of the Johns Hopkins Uni- 
versity, I had last year a series of more than half a dozen 
growths taken from patients suffering from undoubted 
cholera, who had come from Europe in different ships to 
the port of New York during the last cholera epidemic. 
These cultures had been isolated by that able bacteriologist, 
Dr. Dunham, and certainly each separate case presented 
some little difference either in rapidity of growth, in 
amount of pigmentation, in morphological characters of 
the spirilla separating them off’ from Koch’s type. Case 
after case might be recorded of these divergences on the 
part of growths of the cholera spirilla from different 
quarters, the most noticeable being those recorded by 
Sanarelli and by Metchnikoff in connection with spirilla 
taken from various cases in the neighbourhood of Paris. 
The difference between these various growths are as great 
as are those between Koch’s typical spirilla and the spirilla 
obtained from water in regions where no true cholera 
has occurred. Only quite recently, for instance, an 
epidemic not of cholera but of diarrhoea has been described 
as occurring at Lisbon, in which spirilla closely resembling 
the true spirillum of cholera has been isolated. Here again, 
what is the conclusion that has to be drawn ? How is the 
health officer at any point of landing to give an absolutely 
certain bacteriological diagnosis ? Again, take diphtheria. 
Here we are introduced to a slight modification of the 
problem before us. In the case of diphtheria, as in that of 
• It is true that at Berlin they have proved with success that a considerable num- 
ber of these so-called species of Cunningham are only races of the cholera-spirillum 
—nevertheless case after case is being published in which spirilla isolated from cases 
of this disease do not accord in their characteristics with Koch’s narrow limitations 
of the peculiarities of the cholera-spirillum. 8 
suppurative disease (pyaemia) and of pneumonia, not to 
mention yet other examples, that we are dealing with a 
disease due to a microbe of usual pathogenic properties, 
there cannot, in a typical case, be the slightest doubt, yet 
it is possible very frequently to obtain from the healthy 
individual, either from the skin or again from the pharynx 
and mouth, cultures of a form morphologically and biologi- 
cally undistinguishable, from the virulent microbes of the 
above mentioned disease. 
This class of cases, it is true, is not quite so difficult to 
deal with as those previously mentioned, because while 
morphologically the saprophytic forms are undistinguish- 
able from the pathogenic, a clear distinction can be gained 
by experimental inoculation. Animals will take the disease 
and die in the course of a few hours if inoculated with the 
pathogenic form, and will resist inoculation or die only 
after many days if inoculated with the saprophytic form, 
and yet it must be confessed that from a diagnostic point 
of view this morphological likeness does introduce the 
grave difficulty that in order to arrive at a sure diagnosis, 
experimental inoculation must be performed and the bac- 
teriologist must sacrifice a very large number of animals. 
But even this experimental procedure only determines the 
pathogenic qualities of the isolated microbes ; it does not 
wholly settle the question of species. We know both by 
experiment and study of growths obtained from various 
cases that pathogeneity is a variable quantity, just as are 
ferment production and optimum temperature of growth. 
Of course I must acknowledge that in speaking thus I 
am looking and making you look at one aspect of the case, 
but I am doing this purposely, because unless this aspect 
be duly contemplated, there is a danger of wholesale and 
uncertain diagnoses being made, and if bacteriology is to 
be the indispensable adjunct to departments of public 
health, it is urgently necessary that during the next few 
years, while the usefulness of bacteriology in diagnosis is 
under trial, the very greatest care be taken to preclude 9 
hasty and incorrect diagnoses. I acknowledge freely, for 
example, that even without experimental inoculation one is 
generally able to determine by bacteriological methods 
whether a given case is or is not one of diphtheria ; where 
the true disease exists, there the number of colonies devel- 
oping at the end of twelve to twenty hours is relatively 
enormous ; whereas, in a case where the bacillus present is 
not pathogenic the number present upon the surface of the 
medium is very few. 
But making all acknowledgments of this nature that can 
be made, I still believe that what I say is worthy of earnest 
consideration and constant remembrance on the part of the 
bacteriologist. Not until some absolute method for distin- 
guishing between various species of bacteria has been 
elaborated, will bacteriologists be able to make an absolute 
diagnosis in this most important class of doubtful and 
suspected cases. And for my own part I am inclined to 
believe that no such method will ever be devised. What I 
say may, to some at least, appear heretical, nevertheless 
it is my opinion, and I find that it is the opinion of most 
of the bacteriologists whom I have met that with increas- 
ing knowledge there is increasing difficulty in sharply 
defining the various species of bacteria. That this should 
be so seems to me to be only natural, for what are bacteria 
but the very simplest forms of life with which we are 
acquainted, of shape so simple that throughout the whole 
of the group we have but a passage from sphere to straight 
rodlet, to curved rodlet, to spirillum, forms without sex 
and multiplying in the main by fission or division. 
As Weissman has remarked with regard to a similar 
simple form, suppose that an amoeba attached to some small 
particle in a current gains or protects itself by a thickening 
of its ectoderm along the surface exposed to the current, 
then if that amoeba divides, each of the two amoebae will 
possess the same characteristic of the slightly thickened 
ectoderm, and remaining in the same region or under the 
same conditions, all the descendants of this one amoeba 10 
must inevitably possess this same characteristic, and in this 
way a special race of amoebae must tend to be produced. 
So it is with the bacteria, slight alterations of environment 
must affect, and, it has been proved experimentally, un- 
doubtedly do affect the characters of the microbes subjected 
to those changes, and there is an absence of that beneficial 
effect of sexual fusion and reproduction to preserve the 
mean characters of the species. Given any one form of 
microbe it can only retain its special characters over any 
long period of time by retaining a like environment, and 
thus it is that we must expect to find not so much sharply- 
defined species of pathogenic microbes, as fairly well 
defined groups of pathogenic microbes presenting slight 
divergences either in virulence or in morphological charac- 
ters, or in power of fermentation or in all of these condi- 
tions, the microbe varying to a slight extent according to 
variations in environment. In cases of disease that are 
what is termed most typical there we must expect to find 
and to isolate the microbe most nearly presenting 
characters. In our doubtful and difficult cases we must 
equally expect to find microbes departing from the type. 
It may be that in the individual showing atypical symp- 
toms, some peculiarity in his system, some increased or 
lessened power of resistance to the inroad of the bacteria, 
may bring about a modification of the microbe. It may 
be on the other hand that through unusual environment 
the microbes have become modified prior to their entry into 
the system, and thus rendered capable of producing only 
a modified disease. Probably both of these are factors. In 
either case it appears to me that the bacteriologist of the 
future will not so much recognize sharply-defined types as 
he will group together under broad headings, varieties or 
races of bacteria having common characters of growth and 
somewhat similar action upon the organism ; while the 
officer of public health, meeting with a member of one of 
these groups, associated with a not perfectly typical case 
of disease, will treat it as suspicious, and will treat a case 
from which is isolated, not necessarily as one of clearly- 11 
defined disease, but as one worthy of detention and observa- 
tion ; that is to say, in the future it should not be necessary 
to make an absolute and possibly incorrect diagnosis, but it 
will be deemed justifiable to simply state that the case is 
suspicious, inasmuch as the bacteriological evidence is sus- 
picious. As to this grouping of bacteria, there is already 
a fair consensus of opinion with regard to certain patho- 
genic forms ; for example, we recognize broadly a group 
of micrococci producing suppuration, of bacilli causing the 
development of tuberculosis in different animals, of spirilla 
inducing choleriform diarrhoea, of micro-bacilli of acute 
septicaemia in various genera of animals. But we still 
know very little about the relationship of the members of 
the various groups. 
It has seemed to Dr. Wyatt Johnston and to myself, as 
well as to many other bacteriologists, that the best field for 
establishing the laws of grouping is to be found in a study 
of the innumerable slightly varying forms discoverable in 
ordinary water. From the very wealth of the bacterial 
flora in water, the subject of these bacteria in the water 
supply is in an absolutely chaotic state, so chaotic that 
now-a-days one can scarce name and describe a new species, 
for fear lest the slightly different characters given by some 
other observer in some other part of the world, as those of 
a species which he has isolated, be that of some variety 
of the same species. It has seemed to us that the only 
way of emerging out of this chaos is for a series of labora- 
tories to work out each one of the group of microbes ; one 
laboratory, for instance, taking those producing green pig- 
mentation ; another the red pigment bacteria ; another the 
Bacillus Coli Communis with all its varieties in contami- 
nated water. By this means, working out a very large 
number of cultures isolated from regions all over the conti- 
nent, the points of resemblance and of divergence of these 
cultures will best be determined, and as I say from the 
study of a large number of closely-allied forms, it will be 
that the laws of grouping can be determined ; in fact only 12 
by this method can we establish some guidance to lead us 
out of our present difficulties. The scheme, it is true, is a 
large one and may possibly be found impracticable ; never- 
theless we deem it worthy to make the attempt to gain the 
co-operation of others, and we hope that before long, with 
this co-operation of other laboratories throughout America, 
some good work may be initiated m the direction here 
indicated.