FERMENTATION. 117 



state of matters ; first there would be very marked turbidity 

 of the fluid. If we were using a high yeast this turbidity 

 would rapidly become more and more marked, and there 

 would rise to the surface a yellow scum ; bubbles of car- 

 bonic acid gas would be seen rising in the liquid, and a 

 spirituous or alcoholic taste would soOn become pronounced. 

 If from the first fluid, i.e., the fluid in which there was 

 nothing but pure sugar, we were to examine the very 

 minute quantity of yeast, we should find that, although 

 there was apparently an attempt at budding in a few of the 

 cells, in most cases there are a series of clear globules with- 

 in the yeast-cells, that there is a very large proportion of thick 

 walled granular cells (which have certain other peculiarities), 

 that, in fact, throughout the whole we have evidence of very 

 little proliferative activity, and that young, vigorous, healthy, 

 yeast-cells, budding and giving rise to other cells by vegeta- 

 tive activity, are conspicuous by their absence. A micro- 

 scopic examination, in the case of the yeast growing in the 

 sugar solution containing a small quantity of albuminoid 

 material and extractives, reveals a very different state of 

 matters ; here the yeast-cells are in a state of extraordinary 

 activity, buds are being thrown off from the extremities, 

 terminally or laterally, the protoplasm is evidently exceedingly 

 active, vacuolation is conspicuous by its absence, except in 

 certain cells, and we are at once struck by the extraordinarily 

 large proportion of young vigorous cells — the more active the 

 process the greater the number of the new cells, and the 

 larger the quantity of yeast formed. In one case the 

 yeast-cells die of starvation, although large quantities of 

 sugar are present ; and as the yeast-cells have not been 

 able to grow and reproduce by the exertion of their vege- 

 tative activity, they have not been able to resolve the 

 sugar into alcohol and carbonic acid ; badly nourished or 

 dead yeast-cells, therefore, exert little or no influence in 

 bringing about an alcoholic fermentation. In the other case 

 the cells have supplied to them all the elements necessary 

 for the nutrition of their protoplasm. The carbon, the 

 hydrogen, and the water, may all be obtained from the sugar 

 solution, albuminoid material of course supplies the requisite 

 nitrogen, whilst the ash of yeast, which has been added, con- 

 tains all the other elements necessary for the nutrition of 

 the yeast-cells. 



