Period of Incubation 485 



the mirco- organism should be somewhat similar in the different 

 species and should belong to the same genus of bacteria. We 

 would compare the bacteriology of infectious abortion to that of 

 tuberculosis, in which there is a very close resemblance be- 

 tween the bacilli causing tuberculosis in the various species 

 of animals, so much so that the differentiation between certain 

 forms is somewhat in controversy, or at least has only recently 

 been definitely settled. We are strongly inclined to believe that, 

 if the infectious abortion of the cow is caused by a bacillus, that 

 of the mare is also referable to a bacillus ; if the infectious abor- 

 tion of the mare is caused by a streptococcus, as Ostertag claims, 

 the corresponding disease in the cow is likewise caused by a 

 streptococcus. The evidence submitted by Bang and Ostertag 

 is alike good in each case, so far as it goes, nor is there anything 

 definite to show that each may not be correct in his findings. 



There exists the further possibility that the eventual explana- 

 tion of this apparent conflict may rest upon a similar basis to 

 that of hog cholera, where it has recently been admitted, upon 

 high authority, that the disease can be produced in a typical 

 form without the presence of the hog cholera bacillus. This 

 leads one to conclude that the hog cholera bacillus is usually 

 present in hog cholera and may have some secondary relation to 

 the disease or the lesions, and that the essential cause of the 

 disease consists of some micro-organism which has not yet been 

 •discovered. It is so small that it will pass through a filter fine 

 enough to remove the hog cholera bacillus, and the filtrate will pro- 

 duce the typical disease in the hog without the presence of the 

 hog cholera bacillus. It is best, therefore, to accept the re- 

 searches of Ostertag and others as tentative, and to await further 

 researches before finally accepting any conclusion as to the funda- 

 mental cause of the disease. 



The Avenue of Infection. The manner in which the in- 

 fection is carried from one animal to another, and the avenue by 

 which the infection reaches the fetus and its membranes, are 

 highly important, from the standpoint of the control of the 

 •disease. Of first importance is the manner by which the disease 

 is introduced into a herd or stable. According to the observa- 

 tions of Guillerey, which have already been cited, the disease 

 was carried in several instances from one stable to another by 

 anen. Neighbors were called by a client to aid Guillerey in 



