Reprinted from the New York Hectical Journal 
for February 20, 1897. 
THE SERUM DIAGNOSIS OF HOG CHOLERA, 
CHARLES F. DAWSON, M. D., D. Y. S., 
BUREAU OF ANIMAL INDUSTRY, "WASHINGTON, D. C. 
In July, 1896, Widal * described a method which 
he had recently discovered for diagnosticating with ease 
and certainty the existence of typhoid fever. 
The importance of such a discovery is apparent, since 
by this means physicians can ascertain the existence of 
this disease with comparative ease. The method is as fol- 
lows: 
A bouillon culture of the typhoid bacillus is exam- 
ined microscopically to determine the motility and iso- 
lation of the individual bacteria. A few drops of the 
culture are placed in a watch glass and with this is mixed 
a drop of blood drawn from the finger tip of the patient. 
Hanging-drop preparations are then made from the mix- 
ture of culture and blood. A most interesting series of 
phenomena presents itself. The bacilli are not isolated 
and moving as they do in ordinary Cultures, but lose 
their motility and become agglutinated and joined to- 
gether in masses which are separated by wide spaces. 
The clear spaces are dotted with less motile bacilli, and 
* La Presse medicale, July 29, 1896. 
Copyright, 1897. by T). Appleton and Company. THE SERUM DIAGNOSIS OF HOG CHOLERA. 
2 
these can be seen approaching the masses and finally 
adhering to them. Widal observed these phenomena in 
preparations made from patients in difi'erent stages of 
the disease. They did not appear in preparations made 
from the blood of persons in health, and he argues there- 
from the reliability of the test. Nor did the phenomena 
appear in preparations made from patients suffering 
with other diseases—such as nephritis, tuberculosis, 
pneumonia, icterus, and rheumatism; but the bacilli re- 
mained motile, and exhibited no tendency to become 
non-motile and massed together in clumps. 
These very interesting results determined the writer 
to apply the test in hog cholera, a disease resembling ty- 
phoid fever in many respects. In these observations, 
which are preliminary to a more extended investigation 
of the subject, hog cholera was induced in a rabbit by 
the subcutaneous injection of a bouillon culture. 
On the fifth day after inoculation a small piece of 
the ear of the rabbit was excised and clean cover-glasses 
were smeared with the small amount of blood which 
oozed from the wound. No attempt was made to prevent 
the drying of the preparations, and the result obtained 
would indicate that evaporation of the liquid portion 
of the blood does not prevent the appearance of the 
characteristic phenomena. When the preparations were 
perfectly dry, a drop of bouillon culture of the hog-chol- 
era bacillus was placed upon the stratum of dried blood 
on the cover-glass, which was then inverted over a hol- 
low-ground slide and examined carefully with a Zeiss 
two-millimetre apochromatic immersion lens combined 
with a No. 4 ocular. By the time the slide was prepared 
and focused, the bacilli, which had been previously ob- 
served to be motile in a control preparation, became THE SERUM DIAGNOSIS OF HOG CHOLERA. 
3 
motionless and agglutinated in clumps, exactly as was 
described by Widal in reference to the typhoid bacilli. 
A control experiment was made with the blood from 
a normal rabbit, with the result that the hog-cholera 
bacilli did not exhibit the slightest tendency to be af- 
fected in any way. Similar experiments were made 
to determine the effect of hog-cholera blood serum upon 
the typhoid-fever bacillus and the Bacillus coli com- 
munis. The results were negative. The absence of any 
effect of the hog-cholera serum upon the typhoid bacillus 
and also upon the Bacillus coli communis is of interest 
on account of the resemblance of these three organisms 
in other ways. 
Owing to the obscurity of the symptoms usually pre- 
sented in hog cholera, it would seem that a method which 
would render a correct diagnosis would be of considerable 
value, it being by no means an easy task to diagnosticate 
hog cholera from the physical symptoms alone. As it is 
possible that a cure or preventive of hog cholera based 
upon antitoxic-serum therapy will be discovered, it 
would be of great advantage to have a method for de- 
tecting the existence of the disease in its incipiency. 
While the experiments upon rabbits are not offered 
as positive evidence that the same results could be ob- 
tained from affected hogs, it is reasonable to presume 
that a similar result is within the range of probability. 
February 5, 1897.