May 17,1924 
Immunology of Bovine Infectious Abortion 
613 
animals were carried through a third period and gave further evidence of immu¬ 
nity, after a third exposure, by producing living calves and by the absence of 
uterine infection as indicated by the cultural and guinea-pig inoculation work 
that was carried out. 
It may also be observed by reference to Table I that but 3 cows were sub¬ 
jected to the vaccination procedure, the remaining 8 being heifers. The udders 
of these 3 were shown to harbor Bacterium abortus at time of parturition. The 
presence of the infection in 2 of these subjects, 408 and 416, was not demon¬ 
strated previously to the ingestion exposure, in consequence of which it can not 
be assumed that the vaccine treatment was responsible for the condition. Bac¬ 
terium abortus was, however, isolated from the milk of cow No. 410 forty-four 
days subsequently to vaccination and previously to date of ingestion exposure. 
Although this animal produced a living calf at the expiration of a 229-day ges¬ 
tation period, the vaccine treatment is looked upon as probably having been 
responsible for both the premature expulsion of the fetus and the presence of 
Bacterium abortus , which was shpwn to exist in her uterus at time of parturition. 
Animals No. 423 and 401, which gave evidence of having derived some pro¬ 
tection from treatment wdth bacterin, were carried through a second pregnant 
period without further efforts at immunization. Animal No. 423 had received 
11 and animal No. 401, 7 injections of killed abortion bacteria previously to 
first pregnancy. Cow No. 423 aborted at the expiration of 231 days, but failure was 
experienced in demonstrating the presence of Bacterium abortus in either the fetus 
or the other products of the abortion. Bacterium abortus infection of the udder 
was demonstrated in cow No. 401 during and at termination of this pregnancy, 
although its presence in the uterus at time of parturition could not be established. 
OBSERVATIONS WITH REGARD TO SEROLOGICAL TESTS 
Bimonthly applications of the serological tests to the blood serum of the ani¬ 
mals used in the experiment proved to be of interest. It could reasonably be 
inferred from the character of the reactions obtained that in none of the vacci¬ 
nated heifers did Bacterium abortus infection persist for any great length of time 
following treatment. In these animals it was observed that a decrease in agglu¬ 
tinins and complement-fixing bodies began soon after vaccination and gradually 
continued until their blood serum exhibited slight or no agglutinating or com¬ 
plement-fixing properties. Cow No. 410 was the only vaccinated animal that 
continued to react in a pronounced manner to the tests during the entire gestation 
period, and, as previously stated, she harbored the infection in her udder 44 
days subsequently to the treatment. 
The charts of the individual animals (Table V, p. 621) show some degree 
of variation in the results of the agglutination tests that were obtained 
at the different testing dates, as well as between the agglutination and comple¬ 
ment-fixation reactions, particularly in those animals that received injections of 
abortion vaccine. The blood serum of these animals usually possessed some 
agglutinating properties in the quantities employed, when complement-fixing 
bodies could no longer be demonstrated. The results obtained made it appear 
evident that slight reactions to the agglutination test may persist for long periods 
after infection of the animal has apparently been overcome. It is somewhat 
questionable, however, whether the agglutinin content of the sera from the 
treated animals varied from time to time to the extent indicated by the results 
recorded. Slight variations in density of the test fluid employed, a difference 
in the age of the suspensions, a certain degree of variation in the length of the 
period that the tests were incubated, and the personal factor involved in the 
reading of the tests were features that singly or in combination may have been 
largely responsible for such variations in results as the charts indicate. 
The quantities of serum that were used in making the agglutination tests were 
0.04, 0.02, 0.01, 0.005, 0.002, and 0.001 cc. To these quantities were added 
1 cc. of a suspension of abortion organisms similar in density, as determined by 
the use of a Kober nephelometer, to a suspension of barium sulphate prepared 
