SOURCES OF CARBON. 



205 



(2) to replace the energy dissipated by respiration; (3) for the 

 formation of new cell substance in growing cells, or to replace 

 constituents decomposed and excreted, in consequence of other 

 metabolic changes in full-grown cells. The first of these three 

 causes of the consumption of carbon compounds will be discussed 

 thoroughly in a subsequent section, and will therefore be omitted 

 from the present paragraph. The second has also been referred 

 to on pp. 126, 127 of vol. ii., and will be supplemented later; so 

 that we have at present only the third to deal with. 



We are indebted more particularly to EMIL LAURENT (VI.) for 

 a comprehensive investigation of a large number of carbon com- 



ULTIMATE PERCENTAGE COMPOSITION OF THE ORGANIC MATTER 

 OF YEAST REFERRED TO DRY RESIDUE FREE FROM ASH. 



pounds in respect of their suitability for supplying yeast with 

 carbon. These researches were performed on a series of pure 

 culture beer and wine yeasts, with both mineral nutrient solutions 

 and gelatin nutrient media, and showed that the following sub- 

 stances can be absorbed and assimilated as sources of carbon : the 

 acetates of potassium, sodium and ammonium ; lactic acid and 

 the lactates of these three bases and of calcium ; malonic acid 

 and its potassium salt ; succinic acid and its ammonium salt ; 

 the potassium and calcium salts of glyceric acid ; the calcium 

 salt of glycerophosphoric acid ; malic acid and its potassium and 

 ammonium salts ; dextro-tartaric acid and its potassium and am- 

 monium salts ; levo-tartaric acid ; citric acid and its potassium 

 and ammonium salts ; mucinic acid ; f umaric acid ; aspartic acid ; 

 asparagin ; glutaminic acid (all in the proportion of i per cent.) ; 

 glycerin, mannitol, quercitol, glucose, fructose, saccharose, maltose, 

 lactose, dextrin, salicin, amygdalin, and many others. On the 

 other hand, the following were not assimilated by the yeasts (in 

 sedimental and not film cultures) : methyl-, ethyl-, propyl-, and 

 butyl-alcohol (2-4 per cent.), formic acid and its potassium, 

 sodium, ammonium and calcium salts* acetic acid) propionie acid 



