620 
Journal of Agricultural Research 
Vol. XXVIII, No. 7 
positive serological reactions, does not differ so greatly as to suggest that the 
results of the tests were greatly misleading. 
When it is taken into consideration that the agglutination results obtained 
indicated that approximately 60 per cent of these abortions were induced by 
factors other than Bacterium abortus infection, the cause for failure on the part 
of the vaccine in this herd to yield results more in harmony with those obtained 
with animals that were subjected to artificial Bacterium abortus exposure becomes 
more readily apparent. These results emphasize the danger of drawing erro¬ 
neous conclusions as to the value of immunizing agents in infectious abortion 
unless efforts be made to distinguish between abortions of Bacterium abortus 
and other types of causation. 
By referring to the results obtained in the experimental group of 23 animals 
as indicated in Table I, it will be seen that the administration of fetal-stomach 
contents containing Bacterium abortus proved to be a very effective means of 
transmitting the disease to susceptible animals, as all the controls in the group , 
8 in number, were thus infected. In exposure experiments by different investi¬ 
gators who have used Bacterium abortus cultures the percentage of positive 
results has frequently not been so great. It has therefore seemed reasonable to 
suspect either that artificial cultivation of the organism causes a considerable 
reduction in its virulence or that substances of the character of fetal-stomach 
contents, uterine exudates, etc., that contain the infection may act as a protective 
envelope for the microorganisms in the alimentary canal until invasion of the 
tissues occurs. 
The amount of material administered to most of the susceptible control animals 
was presumably greatly in excess of the quantity necessary to cause their infec¬ 
tion, as is evidenced by the fact that 5 cc., 22 cc., and 30 cc. resulted in a manner 
similar to a 60-cc. dosage. 
Viscous uterine exudates heavily saturated with Bacterium abortus have given 
indication of possessing infective properties similar to that of Bacterium abortus 
infected fetal-stomach contents when administered by way of mouth, whereas 
milk in 500-cc. quantities from cows with Bacterium abortus infected udders has 
failed to infect when administered in a similar manner. 
When it is taken into consideration that a single feeding of as small a quantity 
as 5 cc. of fetal-stomach contents proved to be sufficient to produce the disease 
in a susceptible heifer, then it is reasonably obvious why the malady is often 
rapidly disseminated in susceptible herds following exposure to infected subjects 
discharging Bacterium abortus. 
The length of the period that intervened between dates of ingestion exposure 
of the susceptible control subjects and the dates when agglutinins or complement¬ 
fixing bodies could be demonstrated is of practical interest, since it gives some 
idea as to how much confidence should be placed in the serological tests for 
detecting cases of recent infection. This period in the 7 control animals that 
were tested at bimonthly intervals showed considerable variation. The tests, 
moreover, in some cases indicated the presence of specific agglutinins soon after 
their ingestion exposure and their partial disappearance for a period when their 
presence in increasing amount could again be demonstrated. Two heifers (No. 
413 and 446) remained negative to the agglutination test for approximately 4 
months following exposure, and heifer No. 460 for 3J months. A 6 weeks’ interval 
elapsed before serological evidence of infection was obtained in the case of heifer 
No. 450. Blood serum from animals No. 422, 453, and 470 showed agglutinating 
properties in less than a month following exposure. The average length of time 
required for the demonstration of agglutinins was a trifle more than 2 months. 
Somewhat more time was necessary for the detection of complement-fixing bodies 
than of agglutinins, a feature which has been observed in other diseases where 
both methods of diagnosis are used. 
