May 17,1924 
Immunology of Bovine Infectious Abortion 
619 
In this herd 772 vaccinated animals are contrasted with 369 controls. During 
the first gestation period 13.1 per cent of those treated which conceived aborted, 
whereas 17.6 per cent of the successfully bred controls expelled dead calves. 
During the second pregnant period, when records were kept of 311 of the vac¬ 
cinated subjects and 142 controls, 10.2 per cent of the treated animals aborted as 
against 14 per cent of the controls. The vaccinated animals received no immu¬ 
nizing treatment between the two gestation periods. 
In Table IV these 1,141 animals are grouped in such a manner as to give the re¬ 
sults of the treatment of heifers and cows that gave negative agglutination 
reactions at the time they were utilized and animals that gave positive and 
atypical reactions. Reactions were designated atypical when clumping of 1 cc. 
of a Bacterium abortus suspension was caused by 0.02 cc. or 0.04 cc. of blood 
serum but not by lesser quantities. 
Analysis of the figures indicates that the negative heifers derived the greatest 
amount of benefit from the treatment. The treated heifers aborted at the rate 
of 7.9 per cent during the first period and 11.6 per cent during the second, whereas 
the rate of abortions in the controls was 13.6 per cent during the first period and 
18 per cent during the second. 
Treated negative cows aborted at a somewhat lower rate than the controls 
during the first period but at slightly higher rate during the second. 
The abortion rate in the positive and atypical group was exceedingly high 
during the first period. The vaccination of this group gave indication of having 
caused very slight if any improvement in conditions. 
It may be observed by reference to Tables III and IV that when the experi¬ 
mental work in the herd was discontinued sufficient time had not elapsed to 
permit of obtaining complete data on the second gestation periods, subsequent to 
vaccination, of all animals. The percentages of animals which aborted and of 
those which produced living calves during this pregnancy are based upon the 
performance only of those with a second complete breeding history subsequent 
to their experimental use. 
The benefit derived from the use of the vaccine in this herd, even from the treat¬ 
ment of negative heifers, was somewhat less pronounced than was anticipated 
in view of the encouraging results obtained by the same method of immunization 
when negative heifers were subjected artificially to definite amounts of Bacterium 
abortus exposure following vaccination. It was suspected that in this herd 
factors other than Bacterium abortus infection might have been responsible in 
no small degree for the abortion losses sustained, whereupon blood samples for 
the application of the agglutination test were taken from 47 animals that aborted 
after being utilized in the experiment. Thirty of these were included in the 
vaccinated and 17 in the control group. The 30 aborters in the vaccinated 
group gave reactions to the agglutination test as follows: Seven positive, 1 
atypical, and 22 negative. In the control group there were 10 positive and 7 
negative. 
The average length of period that intervened between the dates of aborting 
and the second test was 9i months. Nineteen of the 47 aborters that were 
tested by the agglutination method in less than 4 months following the abortion 
date gave reactions as follows: Eight, or 42.1 per cent positive, and 11, or 57.8 
per cent, negative. The remainder of the aborting group, which consisted of 28- 
animals that were tested between 4 and 23 months after aborting, gave reactions 
as follows: Ten, or 35.7 per cent, positive, and 18, or 64.2 per cent, negative. 
While it is possible that the results of the second tests might have differed ta 
a certain extent had they been made in all cases at or near the time the abortions 
occurred, the percentage of aborters in the two groups, that is, those tested 
shortly following aborting and those after a more prolonged interval that gave 
