168 STUDIES ON FERMENTATIOX. 



spring. Instead of the forms given in Plate X., we have only 

 those represented in Plate XL In other words, the aspect of 

 these ferments changes daily, from the very commencement of 

 fermentation. Thus the yeast would appear to grow smaller, 

 coincidently with the progress of fermentation passing from a 

 condition in which it consists of large cells and long ramified 

 filaments, to a condition in which the cells are small and the 

 filaments short. These changes are principally due to an 

 alteration in the method of budding and in the life-processes of 

 the yeast, which speedily exhibits itself when the air supply is 

 reduced, and not through any intermixture of foreign ferments. 

 So, at least, all our observations up to the present time lead 

 us to believe. As soon as the oxygen has been absorbed the 

 cells which form are oval or globular, and the filaments do 

 not lengthen or become so plump. 



This is, however, not the only cause of these changes in form 

 and aspect, although the presence of air, in greater or less 

 quantity, has a marked influence on the earlier developments of 

 yeast ; there is another circumstance to be taken into account, 

 difficult indeed to state shortly, but which is demonstrated 

 clearly by the microscope, and is connected with the actual 

 state of the germ cells. As a general rule the budding of a 

 cell is not an identical process when the cell is quite young, and 

 when it has become exhausted from want of nourishment. 

 Between these two conditions there is a difierence which may 

 be compared with that which exists, for example, between a 

 newly- formed grain which would not germinate, and the same 

 grain matured by rest, if we may use the expression, that is, 

 which has been kept long enough for its germination to be 

 possible. In other words, and as far as our subject is concerned, 

 we are not to expect that, by reviving our old yeast cells and 

 putting them to grow with abundance of air, in a saccharine 

 nutritive medium, we shall obtain the appearance of the earlier 

 developments of the germ-cells on the surface of sweet and acid 

 fruits. We see this clearly in Plate VII., the right-hand half 

 of which represents the recruited budding of cells, such as those 



