302 MICRO-ORGANISMS AND FERMENTATION. 



as well as albuminoids. Guilliermond showed that by fixing 

 with alcohol and staining with haematoxylin or with methylene 

 blue, some of the granules assume a red colour, whilst the 

 protoplasm is coloured blue. As to their importance to the 

 life processes of the cells, Guilliermond and others at present 

 .assume that they are chiefly of service as reserve material. 

 Glycogen also constitutes an important constituent of the cell 

 contents. It has already been stated that it is assimilated 

 by the cell when it has a rich supply of available carbohydrates. 

 Its presence can be distinguished by a reddish-brown colora- 

 tion with iodine in potassium iodide, whereas the albuminoid 

 substances of the cell assume a yellowish colour. On heating 

 the cell, the brown colour disappears, but reappears on cooling. 

 In the fifth section of this chapter it has been shown that 

 glycogen plays an important part in the auto-fermentation of 

 yeast. 



Ascospore Formation. In 1839 Schwann discovered that 

 yeast cells can form new cells in their interior, and that these 

 .are liberated by the bursting of the wall of the mother-cell. 

 De Seynes gave a clear description of spores in 1868, and in 

 1870 Reess proved that they are produced by yeast cells of 

 different shape, and that the germination of spores takes place 

 by budding. In 1872 Engel indicated moist gypsum blocks 

 .as a specially favourable substratum for the development of 

 spores. Reess, who did not work with pure cultures, regarded 

 these spore-forming yeasts as a special group, which he indi- 

 cated by the name Saccharomyces, a name proposed by Meyen, 

 but he included along with these a large number of species in 

 which no endogenous spore-formation had been observed. 

 .Similar conclusions were published by de Bary in his celebrated 

 work Vergleichende Morphologic und Biologie der Pilze (1884), 

 which also contains admirable observations regarding yeast 

 fungi. 



In 1882-3, Hansen undertook the first experimental in- 

 vestigations concerning spore-formation, and his work made 

 it possible to establish a sharp limit to the group of Saccharo- 

 myces. The results of his investigations concerning the neces- 

 sary conditions for spore-formation may be shortly stated 

 .as follows : 



