148 Agricultural Bacteriology. 



plants to which cattle may have access in the pasture 

 have a like effect on the pregnant animal. 



Contagious abortion or that caused by micro-organisms 

 is more prevalent and more important, since one infected 

 animal introduced into the herd may serve to infect the 

 entire herd. 



Cause. The organism responsible for the trouble is 

 not known with certainty. The disease is undoubtedly 

 most often brought into the herd through the purchase 

 of an infected animal. Once introduced it spreads from 

 one animal to another in various ways. The first case in 

 the herd is not likely to attract attention and hence op- 

 portunity is offered for further spread. Much would be 

 gained if every case of abortion in the herd were treated 

 as though it were contagious. The disease usually disap- 

 pears from a herd in two or three years, in case no new- 

 animals are brought into the herd or young animals do 

 not serve to perpetuate the disease. This has been sup- 

 posed to indicate that an animal becomes immune after 

 two or three consecutive abortions. The abortion usually 

 occurs between the fifth and eighth months of the period 

 of gestation. 



Symptoms. Shortly before the time for the fetus to 

 be expelled, symptoms are shown in varying degree by 

 different animals. The vulva and surrounding tissue is 

 swollen and a yellowish discharge is noted. The udder 

 increases in size. Within two to three days delivery 

 occurs, which is usually accomplished without trouble. 

 If the abortion occurs during the eighth month of preg- 

 nancy, the milk flow will usually be quite normal, at 

 earlier periods the animal gives milk but a short time. 



