300 



MICRO-ORGANISMS AND FERMENTATION. 



the conditions of nourishment of the cells, the development 

 can be promoted or retarded, and the chemical composition 

 modified. The whole behaviour suggests the zoogloea for- 

 mation of bacteria. 



The chemical nature of the wall of the yeast cell is unknown. 

 It is soluble in concentrated sulphuric acid and in concentrated 

 chromic acid. It swells up and becomes transparent in potash 

 and soda solutions. 



SUhT)OXA U 



/.' 



Fig. 50. Yeast cell with gelatinous network (after Hanseu). A, Network obtained by 

 partial drying ; 1, portion formed of threads from which the cells have become detached ; 

 5 and 3 show that the network can also form complete walls, such a formation is seen between 

 a and 6 a is a negative cell, b is a cell with two spores ; U shows three cells, a, embedded in the 

 network. B, network with yeast cells, the latter stained by methyl violet, network is not 

 tained. Some of the yeast cells are still in the meshes, but most have detached themselves. 



The most important part of the contents of the yeast cell 

 is the cell-nucleus, which is not visible in a direct microscopical 

 examination. It can, however, be detected by a suitable 

 micro-chemical treatment of the cell. (The process for its 

 detection is given in Chap, i.) As early as 1879 F. Schmitz de- 

 tected a body in the cell by staining, which was undoubtedly 

 the cell -nucleus. His observations were confirmed and 



