144 MICRO-ORGANISMS AND FERMENTATION. 



ing wort, to which about 5*5 per cent, of gelatine had been 

 added, the flasks being closed by means of cotton-wool plugs. 

 When these flasks are inoculated with the six known species 

 (Sacch. cerevisice /., Sacch. Pastorianus /., //., ///., Sacch. 

 ellipsoideus /., //.), and set aside at a temperature of 25 C., 

 the growths which develop show in the course of eleven to four- 

 teen days such macroscopic differences that four groups may be 

 distinguished more or less sharply. Sacch. ellipsoideus I. 

 stands alone, in that its growth exhibits on the surface a 

 characteristic net-like structure, which enables this species to 

 be distinguished by the unaided eye from the other five 

 species. When gelatine with yeast-water is employed for 

 such cultures and the experiment conducted at 15 C., Sacch. 

 Pastorianus //., after sixteen days gives growths, the edges 

 of which are comparatively smooth, whilst the growths 

 obtained from Sacch. Pastorianus III. are distinctly hairy 

 at the edges. A microscopical examination shows that in 

 this case the two species are also distinguishable morpho- 

 logically. This is not, however, by any means always the 

 case with cultures in solid media ; in fact, the differences are 

 often less marked under such conditions than when nutritive 

 liquids are employed. 



For the Mycoderma species and Sacch. membrancefaciens 

 Hansen has discovered an important characteristic in their 

 behaviour in wort-gelatine, in which they form shield-like 

 colonies readily distinguishable from those of the Saccharo- 

 mycetes. 



In connection with this we may also mention Hansen's 

 observation that some species, e.g., Sacch. Marxianus and 

 Sacch. Ludwigii, can develop a mycelium when grown in a 

 solid medium, whilst others are not able to do so. 



In the case of some cultivated yeasts P. Lindner found 

 distinct differences in their growths on gelatine. 



Will and others have also shown that the characteristics 

 exhibited by cultures on nutritive gelatine are often very 

 variable. 



