150 



Nelson, after the second year's experience with the 

 disease in the herd at the New Jersey Experiment Sta- 

 tion, observed that either the microbe had modified its 

 life habits to better suit the cow or the cow acquires a 

 tolerance for the germ. At any rate, the cow carried 

 her calf longer the second time and often carried the 

 full period the third time. But newly purchased cows 

 were attacked with renwed violence and vouna: cows 

 were more susceptible than old cows. One young cow, 

 1^ years old, aborted 2^ months after conception, and 

 two cows, each 2 years old, aborted at 2 months, 

 while older cows aborted after the fifth month, and the 

 second year no cow aborted under 6 months. 



Immunity. 



This tendency on the part of the microbe and its 

 host to adjust themselves to each other results after 

 two or three abortions in a form of immunity. How- 

 ever immunity in this case is not meant to convey the 

 idea that the cow is rid of the germs, but that she sim- 

 ply will not abort again, while for a long period the 

 germs remain in the womb and may be transmitted to 

 susceptible animals. 



Symptoms. — The first one or two months of preg- 

 nancy abortion occurs without labor pains or straining, 

 and sometimes the fcetus lodges for a few hours in the 

 vagina with portions of the foetal membranes hanging 

 from the vulva or the foetus mav be found in the stable 

 or pasture. If these evidences pass unobserved, the dis- 

 charo;e from the vulva mav be mistaken for heat; but 

 if the cow refuses the bull then, and allows service in 

 due course of time, the evidence, in connection with 

 supposed previous pregnancy, though circumstantial, is 

 quite conclusive that abortion had occurred. Known 



