liOTTOM YKAS'rS. 119 



attrilnjtjiV)lo to tlu* uietaljolism of tin* Vfust ; they uls<j occur in 

 lUiferiniMitiHl wort, iiml in wtut-gi'latiii, iiml, it iniiy be remarked 

 in passinj;, distiul) the beginner wlien he exauiines such h 

 gehitin plate umh-r a low power (30 to 100) before in(K*uhitiii^ 

 with iuicro-or^'aiii>iiis, or eiuployiu',' it for .starting' a siii;.'le-cell 

 culture. Secondly, the yeast mixture contains precipitiited hop 

 resins, in the shape of very small ;,dobules, sometimes united as 

 aggregations ; they give the resin reactions, and therefore 

 assume a handsome retl coloration in presence of alcoholic 

 tincture of alkanna root. Thirdly, there are the so-cjilled 

 ghitin bodies, which are line ghdades of an albuminous nature, 

 originating in the malt and precipitated fi-om the wort at the 

 low temperatuiv (jf the fermenting cellar. They have formed 

 the sul)jeet of some deep researches by 11. Will (111.) 

 Fourthly, certiin dark brown fiagments, which are mostly 

 lookeil on as hop resins by practical brewers, but in reality are 

 said by 11. Will (IV.) to give all the reactions for albumin. 

 When present in large (juantity they form a .source of trouble in 

 brewing, by enveloping the yeast cells and rendering these 

 latter inoperative. The upper layer of the sedimenUil yeast in 

 the vat contjiining the beer in comlition for racking, is 

 specially rich in such extraneous admixtures, and is con- 

 sequently rather dark in colotir. This portion is generally 

 removed in advance and thrown away, before the underlying 

 "white" yea.st is drawn olT. Fifthly come mucilaginous mattens 

 of diiTerent kinds (^ 354 and 255), which have been excretetl 

 bv or extracted from the yeast cells. Sixthly are residual frag- 

 ments of the mashed materials, hops, lupulin granules, and not 

 infrecjuently aphides, and the like. 



It has alreaily been stated that all the Siiniples examined 

 were taken from fresh cultures, /'.»'. cultures in which the 

 primary fernientatit)n was ju.st terminated ami the dej>osited 

 yeast crop was of recent date. On the other hand a diiTerent 

 appearance is prestMited by the cells of a sediment that has lain 

 for some time under the feiinented li«piid~ that is ti> s;iy, in old 

 laboratory cvdtures, or the sludge found at the bottom of lager- 

 beer storage vats, and therefore consisting of cells that have 

 been expo.sed to the influence of the supernatant beer for some 

 eonsiilerabh' time (often .sevenil nmnths). I'nder the.se circum- 

 stiinces a large nundu'r of elongated cells of the I'tisttiriarnut type 

 are produced. I'ven in yeasts that aic ordinarily of <lecide(lly cere- 

 visia- typi'. This is a very useful thing for the beginner t<» know, 

 in order that he may not be disheartened on finding a number 

 of cells of the suspicious PaKtiiHiniun type among the sludge of a 

 vat, the beer in which was fermented with a pure culture yeast. 

 I'rovided the brewing operations have been c«)nductod in a 

 cleanly manner, the pnK'ess of sjxne analysis, de.scribed in § 247, 

 will quickly rejissure him of the absence of infection. 



