474 CHRONIC INFECTIOUS DISEASES 



reaction (incomplete hemolysis) a retest should be made in 

 four to six weeks. A negative reaction does riot necessarily 

 exclude the abortion bacillus as the infection may have 

 occurred so recently that the immune bodies have not yet 

 formed in sufficient aniount to bring about the reaction. 

 The agglutination test is also used. It is found that the 

 blood serxmi of cattle suffering from infectious abortion 

 possesses an average agglutinating value of 1000 and may 

 cause agglutination in dilutions as high as 16,000. In 

 healthy cows the agglutinating value of the serima is rarely 

 above 50. So-called "abortin," which is prepared from the 

 abortus bacillus much as tuberculin is prepared from the 

 tubercle bacillus, has failed to give uniformly satisfactory 

 results. The reaction is a thermic one with which, are some- 

 times associated constitutional symptoms. 



Course. — Infectious abortion usually persists in a herd 

 for years. After the first abortions, often overlooked or 

 attributed to other causes by the owner, new cases occur 

 with a few weeks' interval between. Finally the abortions 

 become more and more frequent until a full-term calf is a 

 rarity in the herd. In time, however, the abortions occur 

 at less frequent intervals. Cows which have aborted one or 

 more times carry to full term (become tolerant — so-called 

 "unmunes"). Clean cows introduced into the herd may be 

 the only ones to abort. Ultimately, in two or three years, 

 the abortions cease entirely, provided the herd has been 

 kept intact. However, there are exceptions to this rule 

 and not infrequently individual cows fail to produce full- 

 term calves. 



Treatment. — Once the disease has gained a foothold in a 

 cow herd, treatment is rarely successful. The reason for this 

 is that the germs of the disease are within the uterus and 

 obviously in the pregnant animal cannot be reached with 

 disinfectants. Very fashionable is the administration of 

 phenol. It may be administered subcutaneously in doses 

 of 10 c.c. of a 2 per cent, solution during the fifth to seventh 

 months of pregnancy or it may be given with the food. A 

 simple method of dosage is to make up a 3 per cent, solution 

 of phenol, giving to each cow daily four ounces of the solution 



Digitized by Microsoft® 



