ALCOHOLIC FERMENTS. 145 



Neither can any conclusions be arrived at by direct 

 measurements of these sedimentary forms. 



A glance at these six 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 this only under 

 the conditions of cultivation indicated. 



(b) Formation of Ascospores. By HANSEN'S work on 

 the formation of endogenous spores in the Saecharomycetes 

 the first essential of an analytical method for the examination 

 of yeast was determined. We add a brief account of 

 the experimental method adopted and of the general results 

 obtained. 



The formation of spores in yeast-cells had been investigated 

 by various naturalists, but the only established result of their 

 numerous and, to some extent, contradictory statements was 

 the fact that Saccharomyces cells could, under certain unknown 

 conditions, form spores in their interim*. 



After making a large number of experiments, HANSEN was 

 able to determine the following conditions regulating the 

 formation of spores in the Saecharomycetes : 



1. The cells must be placed on a moist surface and have a 



plentiful supply of air. 



2. Only young, vigorous cells can exercise this function. 



3. The most favourable temperature for most of the species 



yet examined is about 25 C. This temperature favours 

 spore-formation in all known species. 



A few Saecharomycetes likewise form spores when they are 

 present in fermenting nutrient fluids. 



A growth of yeast is developed in the way described on 

 page 144. Older cultures, developed in saccharose-solution 

 or in wort, must be cultivated several times in aerated wort 

 before showing a normal formation of spores. A small 

 quantity is transferred to a previously sterilised gypsum block : 

 this block takes the shape of a truncated cone ; it is enclosed 

 in a flat glass dish covered by a larger inverted dish, and is 



K 



