194 COMMON AILMENTS OF CATTLE 



which remains for seventy-two hours or longer and disappears 

 very slowly. 



Limitations of the Test. — The tuberculin test should not be 

 applied to cows that have just calved, as the temperature at 

 this time is apt to vary considerably from the normal. Calves 

 under six months of age should not be tested, as their tempera- 

 ture is quite changeable. Cattle in the advanced stages of 

 tuberculosis sometimes fail to react to the test, but such cases can 

 usually be detected by a physical examination. Cattle that 

 have just recently become infected may fail also to react. The 

 tuberculin test, when employed by thoroughly competent men, is 

 by far the most accurate method available for detecting tuber- 

 culosis. The records of large numbers of tests made by govern- 

 ment officials show that the tuberculin test is accurate in ninety 

 to ninety-five per cent of animals tested (Fig. 68). 



INFECTIOUS ABORTION OF CATTLE 



Infectious abortion is a specific infectious disease produced 

 by the germ, Bacillus abortus, and characterized by inflammation 

 of the mucous lining of the uterus (womb) and foetal membranes 

 resulting, as a rule, in the expulsion of the fcetus (calf) in an 

 immature condition. Infectious abortion is known also as con- 

 tagious abortion, epizootic abortion, enzootic abortion, and 

 " slinking " of calves. 



Cause. — The bacillus of abortion, which was described in 

 1897 by Prof. Bang of Denmark, is a short nonmotile rod pos- 

 sessing peculiar physical requirements which make it rather 

 difficult to cultivate artificially. In the diseased cow the organ- 

 ism lives in the mucous lining of the uterus (womb) and it is 

 at times found in the milk of affected cows. Abortion bacilli 

 inhabit the intestinal canal of the affected foetus. Outside of the 

 animal body little is known of the organism. 



The Bacillus abortus is capable of producing abortion experi- 

 mentally in cattle, mares, sheep, goats and swine, by feeding and 

 by injecting the organisms into the circulation. 



Susceptibility. — Infectious abortion is chiefly a disease of 

 heifers, yet in given herds there will be certain periods in which 

 all of the cows Avill abort regardless of age. Infectious abortion 

 does not confine its ravages entirely to dairy breeds, but attacks 



