366 LOUIS PASTEUU 



the influence of the sowing of a mere trace of globules, 

 causes the fermentation of so much sugar?* 



In short, Liebig is not justified in saying that the solu- 

 tion of pure sugar, caused to ferment by means of yeast, 

 contains none of the elements needed for the growth of 

 yeast, neither nitrogen, sulphur nor phosphorus, and that, 

 consequently, it should not be possible, by our theory, for 

 the sugar to ferment. On the contrary, the solution does 

 contain all these elements, as a consequence of the intro- 

 duction and presence of the yeast. 



Let us proceed without examination of Liebig's criti- 

 cisms: 



" To this," he goes on to say, " must be added the decom- 

 posing action which yeast exercises on a great number of 

 substances, and which resembles that which sugar under- 

 goes. I have shown that malate of lime ferments readily 

 enough through the action of yeast, and that it splits up 

 into three other calcareous salts, namely, the acetate, the 

 carbonate and the succinate. If the action of yeast consists 

 in its increase and multiplication, it is difficult to conceive 

 this action in the case of malate of lime and other cal- 

 careous salts of vegetable acids." 



This statement, with all due deference to the opinion of 

 our illustrious critic, is by no means correct. Yeast has no 

 action on malate of lime, or on other calcareous salts formed 

 by vegetable acids. Liebig had previously, much to his own 

 satisfaction, brought forward urea as being capable of trans- 

 formation into carbonate of ammonia during alcoholic fer- 

 mentation in contact with yeast. This has been proved to 

 be erroneous. It is an error of the same kind that Liebig 

 again brings forward here. In the fermentation of which 



It is important that we should here remark that, in the fermentation 

 of pure solution of sugar by means of yeast, the oxygen originally dis- 

 solved in the water, as well as that appropriated by the globules of yeast 

 in their contact with air, has a considerable effect on the activity or the 

 fermentation. As a matter of fact, if we pass a strong current of car- 

 bonic acid through the sugared water and the water in which the yeast 

 has been treated, the fermentation will be rendered extremely sluggish, 

 and the few new cells of yeast which form will assume strange and 

 abnormal aspects. Indeed this might have been expected, for we have 

 seen that yeast, when somewhat old, is incapable of development or of 

 causing fermentation even in a fermentable medium containing all the 

 nutritive principles of yeast if the liquid has been deprived of air; much 

 more should we expect this to be the case in pure sugared water, likewise 

 deprived of air. 





