Infectious, Abortion of the Cow 499 



Many elements serve to confuse the question of the bacteri- 

 ology of infectious abortion. " The normal bacterial flora of the 

 vulvo- vaginal cavity of the cow has not been as fully determined 

 as desired. Nocard has investigated outbreaks of what appeared 

 to be simultaneous contagions of infectious abortion and dysen- 

 teria neonatorum or diarrhea of the new-born. Others have 

 believed that infectious abortion and infectious diarrhea of the 

 new-born were identical. 



The period of incubation of the infectious abortion of cows 

 is as much in dispute as the bacteriology of the affection, and 

 adds to the confusion regarding the latter. Bang makes the 

 incubative period two to seven months. This is wholly out of 

 harmony with clinical experience with infectious diseases in 

 general. Most transmissable diseases show a period of incuba- 

 tion ranging between three and twenty days, so that an incuba- 

 tion stage of eight to twenty-eight weeks naturally causes some 

 doubt. 



Braiier, I,ehnert and others record an incubative period of nine 

 to twenty days. Such a period is in harmony with the incuba- 

 tion period of infectious abortion in the mare and with the 

 incubation period of infectious diseases generally. 



The incubation period of infectious abortion, whether by ex- 

 perimental or natural infection, is probably more variable than 

 most infectious maladies. The infection per vulvam is not 

 direct. We have no definite knowledge of the time required for 

 the infection to traverse the vulvo-vaginal and cervical canals 

 before it can attack the fetal membranes. After the infection of 

 the fetus and its membranes has occurred, expulsion usually 

 does not follow until after the fetus has perished. In the cow, 

 with the rigid cervix, it is not improbable that in many cases, 

 the fetus is retained one, two or more days after its death before 

 its expulsion. Since we generally regard the period of incuba- 

 tion in infectious abortion as extending from the date of expos- 

 ure to the expulsion of the fetus, we evidently include not only 

 the time generally alloted to incubation but also the duration of 

 the disease itself. 



It is highly important that additional observations be made 

 upon the period of incubation. If the infecting micro-organism 

 can live in the gravid uterus, in the fetus or its membranes, for 

 six or seven months, that fact is extremely discouraging in 



