NATURE OF CONTAGIUM. 31 



not universally believed, is yet extensively endorsed and ac- 

 quiesced in by a very large section of the most able observers 

 and investigators in the science of biology. While when 

 adopted and acted upon in its entirety, and to the full extent 

 of its bearings, by us as practical veterinary surgeons and as 

 sanitary inspectors, or conservators of animal and public 

 health, it wonderfully simplifies our actions, and strengthens 

 our hands in dealing with those terribly destructive and 

 harassing scourges which from time to time have devastated 

 communities and nations. 



Arguments have been adduced to prove that at least certain 

 inoculable, contagious, and specific diseases of animals, as 

 glanders in the horse, rabies in the dog, and anthrax in cattle, 

 may be developed spontaneously ; and that in these instances, 

 instead of accepting the theory or view of animate contagia as 

 the actively operating cause, we must turn to our knowledge 

 of the laws of chemistry and physiology for an explanation of 

 their origin. 



The greater and more weighty part of the evidence in favour 

 of the s23ontaneous enzootic origin of the contagious or specific 

 diseases of animals is undoubtedly negative in character, i.e. to 

 say that cases are occasionally met with in which it is im- 

 possible to trace the origin of the particular disease to the in- 

 dividual originating source. This is easily understood when 

 we remember the many and unseen modes by which may be 

 conveyed the active agent of propagation. Cases of zymotic 

 pleuro-pneumonia, or of the contagious mouth-and-foot fever 

 of cattle, regularly occur, in which it is impossible to trace the 

 individual infecting animal ; yet the whole history of these 

 diseases militates against the idea of their being propagated 

 by any other agency than specific contagion, and if for con- 

 tagious lung-fever and zymotic aphtha, so for others of the 

 same class. 



Enzootic and Epizootic Influences. — Although it may be 

 perfectly true, as stated, that contagious diseases must ever be 

 regarded as originating in the action of specific agencies acting 

 from without, whether these consist of malarial emanations, 

 germinal matter separated from previously living animals, or 

 individual living entities, there is at the same time no doubt 

 that, as to their time of appearance, the severity of their indi- 



