May 17,1924 
Immunology of Bovine Infectious Abortion 
609 
in view in undertaking the work was that of procuring additional data with 
reference to the possibilities of immunization, it was also planned to give some 
consideration to the length of time that animals treated with living abortion or¬ 
ganisms carry the infection in their bodies as a result of subcutaneous inocula¬ 
tions. That many noninfected animals might thereby be made carriers or dis¬ 
seminators of the disease seemed possible, in view of the fact that a rather high 
percentage of cows which acquire the disease under natural conditions have been 
shown to harbor the infection in their udders for long periods, and frequently 
eliminate the bacteria from their genital tracts at subsequent parturitions 
irrespective of whether they expel dead or seemingly normal calves. It was pro¬ 
posed in the immunizing experiments to employ both living and killed Bacterium 
abortus organisms, although the value of the latter in rendering animals resistant 
to infection had been seriously questioned by different investigators. 
METHODS OF PROCEDURE 
Two general methods of procedure were followed in applying the immunizing 
tests. In one of these use was made of infected herds where a portion of the 
animals were subjected to immunizing treatments and the remainder employed 
as controls. An attractive feature of this method was that it made available 
for experimentation a large number of animals. Bacteriological studies of 
aborting cows could, however, seldom be made, in consequence of which the 
interpretation of results was rendered somewhat complex and confusing. Impos¬ 
sibility of controlling Bacterium abortus exposure of individual animals under herd 
conditions, moreover, introduced another element of uncertainty. 
In the second method of procedure the number of animals used was limited, 
but it was possible to give more attention to their selection and handling than 
could be done under herd conditions where experimental results were secondary. 
Care was exercised in the procuring of stock which was susceptible to the disease. 
Serological tests were conducted at frequent intervals, and cultural and guinea- 
pig inoculations of milk and uterine materials were made at such times as were 
considered advantageous or instructive. The results that were thereby obtained 
are regarded as being of greater interest and significance than those derived 
from the experiments carried out under herd conditions, and will therefore ,be 
discussed somewhat more in detail. 
EXPERIMENTS WITH SELECTED STOCK 
The stock referred to, consisting of 66 females and 15 bulls ranging from 1 
to 3 years of age, was obtained from an isolated mountainous section of 
Tennessee into which, so far as could be determined, infectious abortion had not 
been introduced. Approximately 20 per cent of the heifers had been bred when 
purchased. Upon subjecting the entire shipment to the complement-fixation 
and agglutination tests negative reactions were obtained in all cases; that is, no 
fixation of complement and no agglutination of a Bacterium abortus suspension 
was produced by 0.04 cc. or lesser amounts of blood serum from any animal. 
Freedom from Bacterium abortus infection was further evidenced by the fact that 
no symptoms of abortion disease were manifested by any of the pregnant heifers 
that were permitted to complete their gestation periods before being used for 
experimental purposes. 
Of the shipment described, 18 heifers and 5 cows were used in the experiment. 
Eight heifers and 3 cows received subcutaneous administrations of abortion 
vaccine 6 when nonpregnant, 4 heifers received abortion bacterin, and 6 heifers 
and 2 cows were used as controls. 
• The term “vaccine” as used in this paper has reference to a suspension of living Bacterium abortus , 
while “bacterin” is used to indicate killed suspensions of the organism. 
