ALCOHOLIC FERMENTS. 125 



mostly elongated sausage-shaped cells. It is, however, a 

 very different matter when cells of the first species are 

 mixed with cells of one of the other species ; it is not 

 then possible, judging from the form alone, to distinguish 

 the larger and smaller oval and round cells of the Pastori- 

 anus species from many of the cells of Sacch. cerevisice. 

 The two species Sacch. ellipsoideus I. and //. consist mainly 

 of oval and round cells ; sausage-shaped cells, however, also 

 occur ; and consequently it is in this case likewise impossible 

 to determine the species by the form of the cells when 

 these are mixed with Sacch. cerevisice or Sacch. Pastorianus. 

 . Neither can any conclusions be arrived at by direct 

 measurements of these sedimentary forms. 



A glance at these six groups of figures of pure cultures 

 shows that we have here three different classes of budding- 

 fungi, one of which is represented by Sacch. cerevisice, 

 whilst the second includes the three Pastorianus species, 

 and the third the two ellipsoid species. This much, but 

 only this much, is possible from a purely microscopical 

 examination, and, it must be pointed out, only under the 

 conditions of cultivation indicated. 



(b) Formation of Ascospores. By Hansels investiga- 

 tions on the formation of endogenous spores in the Saccharo- 

 mycetes the first essential link of an analytical method for 

 the examination of yeast was found. We will give a brief 

 account of the experimental method adopted and of the 

 general results obtained. 



The formation of spores in yeast-cells has been investi- 

 gated by various naturalists ; of the many, and in part 

 contradictory statements, however, the only result which 

 remained as correct was the fact that Saccharomyces cells 

 could, under certain unknoiun conditions, form spores in 

 their interior. 



After making a large number of experiments, Hansen was 

 able to determine the following conditions regulating the 

 formation of spores in the Saccharomycetes : 



