INFLUENZA. 569 



Professor Williams does not state positively what his 

 opinion is on the subject of contagion, and seems to be in 

 considerable doubt on this point ; but as it is not included 

 in the list of contagious diseases in his work on veterinary 

 medicine, I think he must consider it to be a non-contagious 

 disease. 



Cullen, one of the highest authorities on human medicine, 

 declares that influenza, as affecting man, is undoubtedly a 

 contagious disease. 



Professor Smith, Principal of the Ontario Veterinary 

 College, says : — ' I am perfectly confident that influenza 

 is (under certain circumstances) a contagious disease, and 

 may be due to germs so small as to be imperceptible to 

 us.' 



Professor James Law, who has devoted a great deal of 

 time to the study of influenza, is a firm believer in the 

 theory of contagion. 



Now, having, I think, succeeded in satisfactorily proving 

 influenza to be a contagious disease, I will briefly notice a 

 few of the more important views held in relation to the 

 agent or specific material by means of which the disease is 

 propagated. 



There are three principal theories in regard to the 

 nature of the contagium or virus itself It is considered by 

 some to be a ferment void of definite structure, and which, 

 when introduced into the healthy body, is capable of pro- 

 ducing changes in the blood and other fluids. 



Others believe it to be a parasitic organism, originating 

 outside of the body ; but which, on gaining access to the 

 animal economy, is capable of development and increase 

 within it, and probably consists of bacteria. 



The third theory is that the virus consists essentially of 

 bioplasmic granules, possessing amoeboid movement ; or, 

 perhaps, a peculiar species of vital power, by means of 



