206 ORGANIC FOODSTUFFS. 



and its potassium salt, butyric acid, valerianic acid, stearic acid, 

 oleic acid and its potassium salt, sodium butyrate, oxalic acid 

 and its potassium and ammonium salts ; the ammonium salts of 

 benzoic acid, salicylic acid, and gallic acid ; urea (all as i per 

 cent, additions). 



When yeast is cultivated as film cultures on the surface of the 

 nutrient solution, and not under the conditions employed by 

 Laurent, it is also capable of utilising alcohol, though chiefly, or 

 even exclusively, by respiration, a method we are not considering 

 at present. 



Both in nature and in the practice of the fermentation indus- 

 tries, the carbohydrates form the usual and preferential material 

 from which yeast obtains its requirements in respect of carbon, the 

 chief part in this respect being played by certain sugars. The 

 behaviour of yeast toward these latter, with regard to their 

 assimilation as distinct from fermentation, has not, however, been 

 sufficiently investigated, the results of Laurent's researches on 

 this point being unsuitable for generalisation, since they apply 

 solely to the species of yeast tested by him, and not to all the 

 others. We are indebted to BEYERINCK (XVIII.) for the dis- 

 covery that the Schizosaccharomyces octosporus, found by him on 

 currants, forms an exception to Laurent's rule, inasmuch as it is 

 capable of assimilating maltose, glucose and fructose, but not 

 saccharose, lactose, raftinose, arabinose, dulcitol, quercitol, ery- 

 thritol and inositol. The antithesis of this species is Saccharo- 

 myces Zopfii, which, according to ARTARI (I.), can cover its needs 

 in respect of carbon from saccharose, glucose and mannitol, but 

 not from maltose, lactose, galactose, inulose or melampyrit. 

 Similar behaviour to the last-named organism is afforded by a 

 yeast discovered by BEYERINCK (XXI.), and named by him 

 Saccharomyces fragrans on account of the fragrant ester it pro- 

 duces. Sacch. kefir and Beyerinck's Sacch. acetethylicus assimilate 

 glucose, fructose, maltose and saccharose, the last-named one 

 utilising lactose as well. With regard to the suitability of this 

 last disaccharide as a source of carbon, P. MAZE (I.) experimented 

 with eleven stocks of yeast from soft cheese. These few examples 

 will show that, also in respect of assimilation, the only way to 

 obtain really applicable results is by working with pure cultures ; 

 and it is owing to the omission of this essential condition that 

 both the experiments of C. VON NAEGELI (IV.) in the " seventies," 

 and the publications of T. Bokorny and other workers must be 

 left out of consideration here. Dextrin seems to form a good 

 source of carbon for most yeasts; in BEYERINCK'S (XXI.) experi- 

 ments it was only refused by a single species. 



The suitability of the pentoses (C 5 H 10 5 ) as sources of carbon 

 for yeast has not yet been examined by fermentation physiologists 

 as thoroughly as might be desired in the interest of the fermenta- 

 tion industries. The parent substances of these sugars, namely. 



