Il8 BACTERIA. 



Under these conditions, the cells, as we have seen, may 

 undergo rapid development, growth, and multiplication, and 

 we have an increase in the amount of yeast, and at the same 

 time in the amount of alcohol and carbonic acid gas gene- 

 rated. These two experiments afford most exact evidence 

 that Liebig's theory was essentially incorrect, and that 

 Pasteur's theory that true fermentation was the result of the 

 action of the living protoplasm, gives us the key to the whole 

 situation. 



It was, naturally enough, objected that as the fermen- 

 tation process could not go on except in the presence of an 

 albuminoid material, this might really be the cause of the 

 whole process, and many most elaborate experiments were 

 brought forward to prove that it was this organized but 

 dead material that was the real and primary factor in the 

 process. 



Pasteur, however, equal to the occasion, was able to 

 demonstrate in a most convincing manner, that the nitrogen 

 might be supplied to the organism in the form of inorganic 

 salts, instead of being presented as albuminoid material. 

 He utilized for his purposes a mixture containing 1 50 c.c. of a 

 10 per cent, solution of sugar candy, .5 grammes of the ash 

 of yeast, .2 grammes of bitartaric of ammonia, and .2 

 grammes of sulphate of ammonia. He found, on introducing 

 Saccharomyces Pastorianus into this solution, that a some- 

 what slow but very complete transformation of the sugar 

 took place, and that the nitrogen from the ammonia was used 

 up by the growing yeast-cells, which at the same time 

 increased enormously in number. It was thus evident that 

 these mineral salts could take the place, in fermentable liquids, 

 of " media of natural composition." He found, however, that 

 the process went on more slowly, that somewhat peculiar 

 forms of yeast showed themselves, and that an essential factor 

 for the success of the experiment was that no other organisms 

 should be allowed to make their way into the fermenting 

 solutions — i.e., the absolute purity of the various materials of 

 which the nutrient solution was composed, and of the ferment 

 itself, must be guaranteed, and any relaxation of the strict 

 conditions of extreme purity was invariably followed by an 

 interference with the vital manifestations and physiological 

 actions of the yeast organisms. 



It would appear, indeed, that although the fermentation 



