184 MICRO-ORGANISMS AND FERMENTATION. 



paper enclosed in envelopes. 1 HANSEN also found it in the 

 film-formations of nearly all species. An ordinary microscopic 

 examination of the pitching-yeast in a brewery does not show 

 this formation ; with the help of staining, however, its presence 

 can be readily detected (Fig. B). When the yeast is repeatedly 

 washed, it is no longer possible to detect the network by 

 staining ; but if the water is removed, and the yeast set aside 

 for a time and then suitably treated, the gelatinous masses can 

 be readily seen. By varying the conditions of nourishment of 

 the cells, the development can be promoted or retarded, and 

 the chemical composition modified. The whole behaviour 

 suggests the zooglcea-formation of bacteria. 



STRUCTURE AND GENERAL NATURE OF THE 

 YEAST-CELL, 



The usual microscopic appearance of a yeast-cell, as it most 

 frequently occurs in a fermenting liquid, is a spherical or oval 

 figure which gives rise to one or more buds by the swelling out 

 of its wall, these detaching themselves sooner or later from 

 the mother cell. The membrane may vary somewhat in the 

 different stages of development of the cell, but rarely to a 

 noticeable degree. It is otherwise, however, with the contents 

 of the cell. The contents present the simplest appearance 

 when the cell is observed in its most vigorous state of growth. 

 The cell-contents then consist of clear homogeneous plasma. 

 As the processes of multiplication and fermentation continue, 

 different bodies make their appearance in this plasma ; certain 

 clear portions filled with sap (vacuoles), other larger and 

 smaller particles, some of which can be shown to be fat 

 globules, whilst others appear to be of a similar nature to the 

 plasma. These granules have been minutely described by 

 EAUM and EISENSCHITZ. The granular appearance of the 

 plasma increases with the further development of the cell, and 

 at a very advanced stage of the fermentation, when the cell 



1 This method of preserving a sample of yeast for a time is very convenient. 

 A small piece of filter-paper is rapidly passed through a flame several times, a 

 few drops of yeast are poured onto it ; it is then folded up, and afterwards 

 wrapped in several layers of paper which have been similarly treated. 



