99 



tion of bacteria in the presence of various gases supposed to 

 be inimical to life, showing that bacteria can live and thrive 

 in the presence of carbonic oxide, cyanogen, sulphurous 

 anhydride, nitrogen, nitrous oxide, carbonic anhydride, and 

 coal gas. Bacteria were also cultivated by the same inquirer 

 in solutions containing large quantities of salicylic acid, 

 strychnine, morphine, narcotine, and brucine. In all these 

 cases the presence of the bacteria affected in a greater or less 

 degree the chemical results ; the decomposition of cyanogen, 

 for instance, was " assisted " by the bacteria. 



10. — In all these cases it is far from unreasonable to 

 assume that the particular media acted upon may have, in 

 their turns, an influence upon the germs themselves. And 

 although with that strong tendency to see things simply as 

 they are and to avoid generalising, which is, in a peculiar 

 degree, the quality of Pasteur, the author of the modern 

 theory of fermentation has refused to recognise the hypo- 

 thesis of Von Nageli, Buchner, and of Dr. William Roberts, as 

 to the con vertibility of the different species of micro-organisms, 

 he does not expressly deny its possibility, and has, indeed, 

 together with his immediate disciples, demonstrated by many 

 suggestive and remarkable experiments the existence of a 

 certain amount of variability, or adaptability, in microbes. 

 But provisionally, at least, Pasteur rests upon the recognition 

 of a special ferment for each particular kind of fermentation, 

 and what is, in his view, another way of saying the same 

 thing, a special microbe for each zymotic disease ; and the 

 variability which he admits is simply a variability of vigour. 

 With him, moreover, vigour and youth appear to be con- 

 vertible terms, and it is important in following the course of 

 his researches to retain this idea. " Do I deny absolutely the 

 polymorphism of 3Iycoderma aceti 1 " says Pasteur in his 

 " Etudes sur la Biere;" " on the contrary, I have endeavoured 

 many times to establish it. I have sought chiefly for 

 physiological polymorphism, that is, whether Mycoderma 



