xxi.] ANTISEPTICS. 259 



a germicide. There is nothing more fallacious than this 

 method of reasoning ; a great many micro-organisms can be 

 exposed to a i per cent, solution of carbolic acid for hours 

 without in the least being affected, for on being then 

 transferred to a suitable nourishing medium they grow and 

 thrive well. Similarly by placing the spores of bacillus 

 anthracis in a proteid medium containing perchloride of 

 mercury of the strength of i in 300,000, it is found (as 

 Koch has shown) that the spores are absolutely incapable of 

 germinating. But if from this the conclusion is drawn, that 

 perchloride of mercury of the strength of i in 300,000 is 

 a germicide, I should most strongly dissent, for perchloride 

 of mercury of o'i per cent, is not a germicide for all 

 spores any more than vinegar ; for on placing the spores 

 of bacillus anthracis in a proteid medium, to which so much 

 vinegar or any other acid has been added as makes it 

 decidedly acid, it will be found that the spores do not 

 germinate. 



In order to pronounce a certain substance a germicide in 

 the strict sense of the word, it is necessary to place the 

 organisms in this substance for a definite time, then to 

 remove them thence, and to place them in a suitable 

 nourishing medium ; if they then refuse to grow the conclu- 

 sion is justified that the exposure has injured or destroyed 

 the life of the organisms. In the case of pathogenic 

 organisms a substance to be pronounced a germicide must 

 be shown to have this power, that when the organism is ex- 

 posed to the substance and then introduced into a suitable 

 artificial medium it refuses to grow; and it must also be 

 shown that when introduced into a suitable animal it is in- 

 capable of producing the disease which the same organism, 

 unexposed to the substance in question, does produce 



I have made a good many observations on the influence 



s 2 



