i8g6. NOTES AND COMMENTS. 75 



JMiddle Atlantic slope or from other better known formations, are to 

 be regarded as something more than counters for the stratigraphical 

 geologist to gamble with. We will not insist upon illustrations, but 

 if these are not given it is all the more necessary that the description 

 should clearly convey the appearance of the species. Still, though we 

 make this concession, we urge again that what is really wanted nowa- 

 days is careful and detailed work, accompanied by a thorough 

 revision of all the imperfect and inaccurate statements launched upon 

 the world, chiefly in the form of preliminary notices. 



The Variation of Yeast-Cells. 



The Annals of Botany (vol. ix., no. 36) contains a short account of 

 some experimental studies on the variation of yeast-cells by Professor 

 E. C. Hansen, of Copenhagen. Professor Hansen had already shown 

 that the form and size of the cells cannot be used alone, as was done 

 by Reess, to characterise species ; for from each of the species it is 

 possible to produce the rest by varying conditions of cultivation. 

 Thus the large oval cells, characteristic of Saccharomyces cerevisia, the 

 beer-yeast, under favourable circumstances of nutrition, may be 

 developed by wine-yeasts with small oval cells, Reess's 5. ellipsoideus, 

 and the converse change may also be effected. Again, the sausage- 

 shaped cells of 5. Pastorianus can be produced in several ways from 

 the other two yeasts. There are many reasons which make it 

 probable that the oval form is the primitive. 



Hansen has also shown that cultivation for a long time in 

 aerated wort, at a temperature above the maximum for spore- 

 formation and approaching that for vegetative growth, causes a 

 complete and permanent loss of the powers of spore-formation, and of 

 producing films on the surface of liquids. The loss of the latter 

 property causes a marked alteration in their influence upon the 

 liquids in which they grow ; the cells of the film which develops on 

 fermented beer-wort cause the liquid to become lighter in colour, and 

 also produce a vigorous oxidation by which the alcohol is broken up 

 into carbonic acid and water. Thus, while an ordinary yeast-culture, 

 left to stand for six months, contained only 1-5 per cent, of alcohol in 

 the fluid, that of a non-film-producing variety obtained from the same 

 stock showed an alcohol percentage of 5*5, that is, the same amount 

 as at the end of the first month. By cultivation on the surface of 

 nutritive gelatine, varieties were developed having a greater 

 fermentative power than their primitive forms, in one case amounting 

 to the production of as much as 3 per cent, more of alcohol. Another 

 experiment which has an economic bearing shows an effect of the 

 chemical composition of the nutrient liquid. S. Pastovianus is one of 

 the disease-yeasts of beer, imparting an offensive odour and a 

 disagreeable bitter taste. When cultivated for a number of genera- 

 tions in a solution of cane-sugar in yeast-water, a growth was 



obtained which for a time had lost these properties. Frankland and 



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