426 PROTECTIVE INOCULATION FOR BOVINE PLEURO-PNEUMONIA, 



tuberculosis, the microbes of which represent the vehicles of 

 both direct and indirect infection, the latter taking place by 

 germs (their spores) which exist in our surroundings, and hold 

 out there for a considerable length of time. (2) The disease, 

 as such, might be attributed to so-called facultative parasites, 

 i.e., micro-organisms which feed, multiply, and may form resting 

 stages on or in various dead organic substances, but transferred 

 to the living animal body manifest themselves as parasites. 

 The best known instance of such a case is furnished by anthrax or 

 splenic fever. The pathogenic agents of this infectious disease, the 

 antlhrax bacilli, are not necessarily bound to live in animals or in 

 man ; on the contrary they are originally harmless saprophytes, 

 Ijiit, when occasionally gaining access to the blood-system of living 

 beings, they unfold a most pernicious activity. 



It is evident that a decision of which of the above conditions is 

 fulfilled with regard to boviue pleuro-pneumonia, nmst have a 

 legitimate bearing on the question of the kind of protective means 

 to be adopted against the disease. If this is inaugurated after 

 the manner of syphilis, and therefore, the scope of its spreading 

 very much limited and easily traceable, then it would be most 

 questionable whether some preventive vaccination should be pre- 

 ferred to other prophylactics. If on the other hand there are far 

 more dangerous doors oi:)en to the propagation of the disease, and 

 if we have reason to suppose that it depends on a contagium like 

 that of tuberculosis or of splenic fever, then, of course, the subject 

 of protective inoculation claims a greater interest. 



Unfortunately our knowledge of the exact manner in which 

 pleuro-pneumonia makes its appearance and spreads, is as yet far 

 from being certain ; nor are we warranted in arriving at a satisfac- 

 tory answer so long as the causal factors of the plague are not 

 yet thoroughly recognised and their biological properties studied. 

 What we may gather from practical observations is not sufficient 



