BY DR. OSCAR KATZ. 425 



is altogether olijectionable from a practical standpoint as well as 

 from an economical one, and that consequently, all therapeutics 

 have to be thrown overboard. Nothing then remains but the 

 employment of prophylactic measures, of which protective inocu- 

 lation is one. We have now to enter upon a consideration of the 

 nature of this subject, and to see whether the results of such a 

 consideration can be bi'ought into harmony with the seemingly 

 favourable results claimed by the advocates of the system. 



The notion " protective inoculation " in connection with any 

 disease, hence also in the cattle disease under notice, pre- 

 supposes that it belongs to the group of infectious diseases which 

 by means of a " contagium," are capable of transmission from 

 individual to individual, at least under certain circumstances. 

 That bovine pleuro-pneumonia is one of this kind, or in other 

 woi'ds, that it presupposes a contagium in the shape of an 

 organised something, of a microscopic being, is regarded as 

 a settled question, to judge from the present standpoint of 

 science, and from practical experience. For a full understanding 

 of the disorder, as well as for the mode of combating it (taking 

 special reference to protective measures), it must, however, 

 appear very important to know at the very outset, how the disease 

 spreads. There are two principal possibilities. (1) It may be 

 caused by germs which represent so-called obligate parasites, that 

 is to say, which for their propagation need the body of cattle 

 (or perhaps of some other animals). These germs again might 

 be of two descriptions. On the one hand they might lose their 

 power of infecting by having been exposed to external agencies, 

 tlius resembling, as it were, the pathogenic factors in human 

 syphilis, in regard to which we are compelled to accept the view 

 that it cannot be communicated but by immediate contact. On 

 the other hand they might also, after having left the animal 

 body, but if so without being able to propagate, possess the 

 faculty of infection. An instance of such a kind we have in 



