166 DISEASES OF CATTLE. 



healthy, pregnant cows by the introduction of exudate and material 

 from aborting animals. Nocard (1888) isolated from the exudate 

 between the mucous membrane of the uterus and fetal membranes 

 a micrococcus and a short bacillus which were found continually 

 in contagious abortion, but he failed to reproduce the disease by 

 inoculations of pure cultures of these organisms into healthy, preg- 

 nant animals. In 1897 Bang, assisted by Stribolt, published their 

 findings regarding infectious abortion of cattle, in which they in- 

 criminated Bang's bacillus of abortion as the causative agent. With 

 pure cultures of this bacillus they were able to produce the disease 

 artificially and to recover the same organism from the experimental 

 cases. Since that time many noted investigators, both in this country 

 and in Europe, have confirmed these findings. 



Cause. — The Bacillus abortus of Bang is now generally recognized 

 as the causative agent of the disease of cattle. Formerly it was 

 thought that abortion was due to injury, such as blows, horn thrusts, 

 falls, etc., or the eating of spoiled feed and certain plants, and while 

 this may be true in a limited number of cases, careful investigations 

 have demonstrated these claims to be largely unfounded. It is now 

 generally recognized that when abortion occurs in herds from time 

 to time, it is safe to assume that the disorder is of an infectious 

 nature and should be so treated. 



Natural mode of infection. — This phase of the disease is of greatest 

 importance for a clear understanding of the methods of prevention. 

 Many investigators claim to have demonstrated that the infection is 

 transmitted through the digestive tract, by consuming contaminated 

 feed and water. The germs are taken up by the body from the in- 

 testines with the liquid nourishment, reach the blood, and are carried 

 to the genital organs, where they find conditions best suited to their 

 development. Some assert that calves are infected in this manner 

 by suckling infected mothers, the germs being jDresent in the milk, 

 or the teats having been contaminated by coming in contact with in- 

 fective discharges. It is claimed that infection contracted in this 

 manner remains dormant in the body of the calf until pregnancy 

 begins, and then the organism, finding conditions suitable for its de- 

 velopment, produces the disease. 



Abortion may be transmitted from cow to cow by direct contact. 

 The discliarges from diseased cows, swarming with the germs, soil 

 the external genitals, tail, and hind, quarters, and then a susceptible 

 animal, by contact, gets the infective material upon the vulva, the 

 infection traveling up the genital canal and directly infecting the 

 uterus. 



The most important and most frequent mode of infection, however, 

 is that occurring through the act of copulation. The bvdl, having 

 become infected by serving an infected cow, carries the infection 



