IJOTTOM YEASTS. 113 



jjarten's Jahregheriflil. These species are oftt* iitiuies spukeii of 

 as Sarcharomyre^, or yeust, altliouj;lj their connection with thin 

 •jenus, or their f;ioulty of exritin^ feruientation, is more or less 

 doubtful. This reiuiirk applies to the st>-e;illtHl Surrh. j'arri- 

 ininosim TukUhiijf, SarrJi. iieofunnatig, and Saccfi. lit/ioi/tTiejf San- 

 r'elire ; Sarr/i. splinriiius iind SivrJi. (/ml in run J/(M>ni, iVc. One 

 species reco^fuiseil as exciting fennentjition, and consequently 

 to be classed as a yeast, thou<.'h not as yet proved to be a true 

 Sacrharomyres, is a budding fungus discovered by O. liusse, and 

 observi'd by him to iiroduce, in tln« human body, a kind of general 

 de]>ility i^SiVrharinnyi-usii') which may terminate fat;illy. That 

 certiiin true yeasts are pathogenic when artificially introduced 

 int(j the arterial circulation, was proved in 1S92 by Hut-ppe, in 

 the course of expoiiments with Rauenthal wine yeast and young 

 porpoises. This result has been repeatedly confirmed since, 

 notiibly by L. Uabinowit.-ch, in a .series of experiments with 

 about fifty stocks of dilferent species and origin, .seven of which 

 proved pathogenic. 



§ 245.— Bottom Yeasts. 



If a number of flasks be charged with a clear nutrient solu- 

 tion, of a kind favourable to the growth of yeast and containing 

 a ferment;ible sugar, and each of them be inoculated with a tnice 

 of a pure culture of dilferent yeasts, such as are useil in brewing, 

 distillery work, vinification, Ac, the cultures being then kept at 

 room tempeniture for a couple of days, it will be found that cell 

 reproduction and fermentiition — manifes^ted l)y the appearance 

 of turbiditv and ;'as bul)bles— will occur in all. It will there- 

 after soon be po.ssible to sepanite the flasks into two groups, 

 according to the appearance pre.sented. In the one group the 

 vaist crop developed from the .sowing will remain almost entirely 

 within the licpiid throughout the entire periml of fermentation, 

 and mostly at the bottom even from the start. Yejists of this 

 kind are termed bottom yeasts, and excite bottom -fermentation, 

 the yeast crop l)eiug se<limental. 



In the other group the fermentiition is very lirisk and 

 attended with the formation of largo (juantities of fix)th (head) ; 

 and in the earlier .stiitres a larger or smaller number of the new 

 cells are raised to the surface by the a.^cending bubbles of gjis, 

 and remain there — proviiled the vessel be high enough to pre- 

 vent frothintr over until fermentation is terminati-d and the 

 froth breaks up, whereupon they sink down to the iKUtom of the 

 liquid and increase the .sedimentiil deposit. This kind of fer- 

 mentation is termed top fermentation, ami the yejvst.s j)roiluc- 

 ing it are called top-fermentation yeasts. Typical examples 

 of bottom - feruKMitat ion yea.'>ts are .ilTorded by the Munich 

 lager-beer yeasts. On the other hand, the most highly 



VOL. II. H 



