168 DISEASES OF CATTLE. 



retained membranes decompose, the poisonous products of decompo- 

 sition and the organisms of decomposition themselves are absorbed, 

 blood poisoning results, and the animal dies. Sometimes, Tvhen the 

 animal is able to resist the effects of this decomposition, the uterus 

 becomes the. seat of such severe changes that sterility results. The 

 walls of that organ become thickened and hard, the lining mem- 

 branes become eroded, and conception can not take place. At other 

 times the ovaries, where the reppilductive cells originate, become 

 affected and lose their function. Abortion does not invariably fol- 

 low infection, but the calf is carried to full term. In these cases, 

 however, retained afterbirth is a common occurrence, even to the 

 extent that frequent retention of afterbirth in a herd may be taken 

 as an indication of the presence of the disease. Very often sup- 

 purative processes persist for a long time, preventing conception, or 

 sterility may result without apparent cause. A sterile cow is value- 

 less, of course, for any purpose except for beef. Such animals are 

 a source of infection for the others and should not be allowed to 

 remain in the herd. 



Diagnosis. — The diagnosis of infectious abortion is made from 

 the changes occurring in the fetal membranes and in the expelled 

 fetus. This, however, is substantiatecTwith certainty only by micro- 

 scopic demonstration of the germ of abortion. The fact that re- 

 peated abortions are observed in a herd is also evidence of the 

 presence of the disease. In consideration, however, of the fact that 

 animals may be affected with the disease and disseminate the germs, 

 even though they carry the fetus to full time, a diagnosis in such 

 instances is only possible by laboratory methods. For this purpose 

 the agglutination and also the complement-fixation tests are being 

 used with splendid results, and by the aid of these biological tests 

 it is possible to determine all infected animals in a herd. The tests 

 are carried out with the serum from animals to be examined, only 

 a teaspoonful of serum being necessary for the execution of both of 

 these tests. It, however, has to be confined to laboratories which are 

 properly equipped for such work. 



Treatment and 'prevention. — It may be said in general that treat- 

 ment is without aA^ail and all efforts should be directed toward pre- 

 vention. Various medicinal agents, such as carbolic acid adminis- 

 tered subcutaneously and methylene blue fed in large quantities, 

 have been recommended, but have failed to stand the tests of scien- 

 tific investigation and practical use. Serums and vaccines have 

 also been prepared and sold as cures and preventives, but the work 

 is still considered in the experimental stage. 



Bacterial vaccines are at present extensively used in the control 

 of this disease, and while numerous reports indicate beneficial re- 



