XXL] 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 



