MORPHOLOGY AND ANATOMY OF YEAST CELLS. 297 



yeast-cells germinate from the resting cells, either singly or 

 in large number (Fig. 49, A). Club-shaped cells with trans- 

 verse-wall formation frequently arise, especially in older 

 cultures of resting cells produced in mineral nutrient solution. 

 This phenomenon may recur in derived growths (Fig. 49, B). 

 During germination on a solid nutrient medium, Will also 

 observed a splitting up of these transverse walls (Fig. 49, B). 



According to Rayman and Kruis the cells of the film have 

 a, marked respiratory power, oxidising the alcohol formed into 

 carbon dioxide and water, and at the same time splitting up 

 the albuminoids of the liquid into amides and ammonium 

 salts of organic acids. 



Cultures on Solid Substrata. After Schroeter and Koch 

 had shown that by cultivation on solid media, species of bacteria 

 display distinct characteristics, Hansen succeeded in proving 

 that a similar relationship holds good for yeasts. For this 

 purpose he utilised beer- wort, to which about 5- 5 per cent, of 

 gelatine had been added, contained in flasks closed by means 

 of cotton- wool plugs. When these flasks are inoculated with 

 the six species (S. cerevisice /., S. Pastorianus /., //., ///., 

 8. ellipsoideus I., II.), and allowed to stand at a temperature 

 of 25 C., the growths which develop (streak-cultures) show 

 such macroscopic differences in the course of eleven to four- 

 teen days that four groups may be more or less sharply dis- 

 tinguished. S. ellipsoideus I. stands alone, for its growth 

 exhibits a characteristic net-like structure on the surface, 

 which enables it to be distinguished from the other five by the 

 unaided eye. When gelatine with yeast- water is employed 

 for such cultures and the experiments conducted at 15 C., 

 jS. Pastorianus II. yields growths after the lapse of sixteen 

 days, the edges of which are comparatively smooth, whilst 

 the growths obtained from S. Pastorianus III. are distinctly 

 hairy. A microscopical examination shows that the two 

 species are also distinguishable morphologically. This is by 

 no means always the case with cultures on solid media ; in 

 fact, the differences are often less marked under such condi- 

 tions than when nutritive liquids are employed. 



For the Mycoderma species and S. membranes faciens, Hansen 

 discovered a characteristic behaviour in wort-gelatine in which 



