176 CHEMISTRY OF THE YEAST CELL. 



may be simviltaneously present in one and the same yeast, 

 whether of the top- or bottom-fermentation variety. This 

 worker boiled yeast over a naked flame three times in succession 

 for six hours each, in Avater containing a small addition of lime, 

 then precipitated with ammonium oxalate the lime from the 

 filtered extract, filtered and concentrated the solution, faintly 

 acidified it with hydi'ochloric acid, and treated it with an equal 

 volume of 96 per cent, alcohol. The resulting precipitate 

 of brown gum was decolorised by washing with alcohol, and 

 was found to exhibit a percentage composition corresponding 

 to the formula C^H^QOg. The gum from top - fermentation 

 yeast had the rotatory power cId = + 283.7°, that of the pro- 

 duct from bottom - fermentation yeast being -f 287.6'. The 

 precipitate thrown down from the aqueous solution by Fehling's 

 solution had the composition 2(C,.H-,,p^).CuO.HoO. This gum 

 furnishes on hydrolysis, not one sugar only but two, namely, a 

 little glucose and a large quantity of J-mannose ; it therefore 

 chiefly (but not exclusively) consists of mannan, the percentage 

 of which, referred to the dry residue of the yeast, amounts to 

 6-7 per cent. 



E. Salkowski (V.) classed as in the main identical with 

 this mannan the yeast gum which he obtained in 1894 by 

 boiling pressed yeast for half-an-hour with a tenfold volume of 

 3 per cent, caustic potash. This treatment brought into solution 

 the whole of the cell contents, including the gum. When cold 

 this extract was syphoned off from the residue (of so-called 

 yeast cellulose), treated with 15 per cent, (vol.) Fehling's re- 

 agent, well mixed and heated. The blue copper compound of 

 the gum separated out in lumps, which were immediately 

 taken out, rinsed with a little water, triturated in a basin with 

 a few drops of hydrochloric acid, and thus converted into a 

 cloudv liquid, from which the gum could be thrown down by a 

 three- to four- fold volume of 96 per cent, alcohol. Repeated 

 solution and re-precipitation finally gave a white, ash-free mass, 

 which was dried with alcohol and ether, and then amounted to 

 about 7 per cent, by weight of the dry residue of the yeast. 

 The results of the ultimate analysis corresponded to the formula 

 CjoHooOj^. In contradistinction to the yeast gum obtained by 

 Keegeli and Loew, this product dissolved readily in water to a 

 filterable, but very glutinous liquid. The sugar furnished by 

 the hydrolysis of this gum seems to have been regarded by 

 Salkowski as r/-mannose. 



Na^geli and Loew thought themselves justified in assuming 

 their yeast gum to be a conversion product of the yeast cell 

 membrane, because they found that fresh quantities of this gum 

 could be obtiined from beer yeast by repeated boilings in water, 

 the total amount (including the so-called cellulose) being about 

 37 per cent, of the dry yeast. It was then found by E. Sal- 



