IN CONTAGIOUS VIRUS. 



certainly be the case if the particles present in the fluids 

 had been vegetable germs. Every kind of parasitic 

 germ known is capable of undergoing development 

 into a body having definite and well-marked -charac- 

 ters. Though in the germ stage different species 

 would resemble one another, as indeed is the case as 

 regards creatures much higher in the scale, they do not 

 constantly retain indefinite characters. And when the 

 germs are so minute as to be readily passed over in 

 ordinary microscopical examination ( 100 to 300 ), by 

 the aid of higher powers excessively minute vegetable 

 germs may be recognised with certainty, if not by 

 their form, at least by their mode of multiplication. 

 The germs of many animal parasites are also to be 

 distinguished by careful examination, and from what 

 we know of the life history of these, we should not be 

 justified in attributing contagious diseases, in which 

 every drop of animal fluid in the body possesses con- 

 tagious properties, but for a fixed and definite period 

 of time only, to germs of a new class of animal or 

 vegetable parasite of which not one species has 

 been discovered, and the germs of which are even 

 less than TO oV'oo- f an mc ^ ^ n diameter. It may, 

 therefore, be affirmed that the matter which forms 

 the active virus or poisonous material does not 

 exhibit the properties of any vegetable or animal 

 parasitic organism yet discovered and identified. 

 Neither can any organisms, having special and pecu- 

 liar characters, be developed from any definite virus. 



