May 17, 1924 
Immunology of Bovine Infectious Abortion 
617 
from the milk samples, in no instance could the presence of abortion disease be 
demonstrated in the guinea pigs when they were destroyed, April 12, 1922, 
although serological and cultural tests were conducted. 
Another group of 11 cows that gave negative results to the agglutination test 
was vaccinated November 17, 1921. Samples of blood and milk were obtained 
from these animals June 24, 1922, and tested by the agglutination method. In no 
case did any of the milk samples show agglutination with 0.04 cc. or lesser amounts. 
The blood serum of 3 animals showed slight clumping in 0.01 cc. quantities. The 
serum reactions of the remaining 8 were either negative or showed a titer of less 
than 0.01 cc. Two guinea pigs were injected with 4 cc. of milk from each cow 
of this group. When destroyed, two months later, all the pigs yielded negative 
serological and cultural results for Bacterium abortus. 
When consideration is given to the results obtained with the 23 animals that 
were used in a purely experimental capacity, it seems important to bear in mind 
that so far as could be determined they were free from Bacterium abortus infection 
and susceptible to the disease, and, furthermore, that the vaccination procedure 
gave indication of being successful only when temporary infection of the animal 
was occasioned by the treatment. Our knowledge of immunity with reference to 
other diseases enables us to conceive how under these conditions the administra¬ 
tion of abortion vaccine may constitute a reasonable and rational immunizing 
procedure. 
Abortion bacterin failed to show highly encouraging results in this experiment. 
Although 2 of the 4 animals utilized successfully withstood Bacterium abortus 
exposure that caused controls to abort, it should be borne in mind that this 
product was used under what may be regarded as ideal conditions; that is, 
noninfected heifers were used to test the efficacy of the method, and repeated 
injections of generous amounts were made not only previously to exposure, but 
in the case of one aborter 4 times previously to conception. Indication that the 
immunity derived from the bacterin treatment was of but low degree and tran¬ 
sient is evidenced by the fact that cow No. 401 acquired Bacterium abortus udder 
infection following her second ingestion exposure. Although failure was experi¬ 
enced in demonstrating that bacterin-treated animal 423 was infected with 
Bacterium abortus following her second exposure, the character of her serological 
reactions indicated that such may have been the case. 
VACCINE TREATMENT UNDER HERD CONDITIONS 
Abortion vaccine has been used in a number of infected herds with the object 
of acquiring further information as to the practical value of such a product in 
combating the malady. The interpretation of results under these conditions has 
not been wholly satisfactory, since, as has been previously mentioned, the matter 
of Bacterium abortus exposure could be controlled only in a measure, and because 
it has seldom been possible to conduct the necessary bacteriological work during 
such investigations to permit of differentiating between abortions of Bacterium 
abortus causation and those induced by other factors. Brief consideration, 
however, will be given to one herd consisting of more than 1,500 head of dairy 
stock, in which the disease had been prevalent for a number of years, and in 
which the vaccine was used for the treatment of the nonpregnant animals. 
As animals in this herd became available for treatment blood samples were 
obtained for the application of the agglutination test. Available animals included 
open cows that had freshened at least two weeks previously and heifers that 
were within two or three months of breeding age. Two-thirds of the subjects 
from which blood samples were taken, which group included positive and atypical 
reactors as well as negative animals, thereupon received a subcutaneous in¬ 
jection of 20 cc. of vaccine, the remaining one-third being employed as controls. 
The results derived from the utilization of 1,141 animals under herd conditions 
are indicated in Tables III and IV. 
