SCHIZOMYCETES AND SACCHAROMYCETES 301 



All saccharine fluids which contain glucose, or grape sugar, 

 or a sugar which can be changed into glucose, and also 

 all nitrogenous substances, phosphates, and ammoniacal salts, 

 produce alcohol at a given temperature. The process of con- 

 version is by fermentation. Pasteur states that every 

 fermentation has its specific ferment ; in all fermentations in 

 which the presence of an organised ferment has been ascer- 

 tained that ferment is necessary. This minute being produces 

 the transformation which constitutes fermentation, by breath- 

 ing the oxygen of the substance to be fermented, or by 

 appropriating for an 



instant the whole _Q q^^ ^ ^V) 



substance, then de- C5 © @^ ^ Q-^y rp 

 stroying it, by what ^<||) © ^ cC^p^^^ ^>' ^b 

 may be termed the ^ ^J O 



secretion of the fer- ^ ,„„ ,,„. , ,„ ,,, ^, , ,„. , 



Fig. 139. — ' High yeast. Chatto and Wmdus. 



mented products. 



Three things are necessary for the development of the 

 ferment — nitrogen in a soluble condition, phosphoric acid, 

 and a hydrocarbon capable of fermentation, such as grape 

 sugar. The common ferment of wine has elliptical cells, but 

 there are other forms, or species, which are capable of pro- 

 ducing fermentation in wine. The yeast of beer has round or 

 oval cells,^ and so on, through the range of species, of which 

 Saccardo enumerates thirty-one (Fig. 139). 



It was contended at one time that these ferments were 

 derived from moulds and Mucors, which under favourable 

 conditions continued to increase themselves by budding — viz. 

 simple vegetation — but, if deprived of nutrition, produced the 

 fructification of a mould. De Bary, whilst controverting this, 

 suggests that some yeast cells have probably been mixed with 

 the spores sown in a nutritive fluid. He thus describes the 

 development of yeast, beyond the ordinary vegetation in a 

 fermentable solution : " If we bring living cells of yeast out of 

 the fluid, on the moist surface of a succulent part of a plant — 

 for example, a piece of carrot — the sprouting goes on slowly for 

 some time, and entirely ceases after some days. About the 

 sixth day, we remark how some of the cells wither and others 



1 Microbes, Ferments, ami Moulds, by E. L. Trouessart, London, 1889. 



