224 CULTIVATION AND REPRODUCTION OF YEAST. 



(XXIV., V.) retained their vitality for many years (up to seven- 

 teen). Sacch. Ludwigii proved less hardy, some of the samples 

 dying within one-two years, though others lasted six years ; and 

 Carlsburg bottom yeast No. 2 behaved in a similar manner. To 

 these exceptions must be added the Sacch. theobromce isolated by 

 A. PREYER (I.) from putrefying cocoa, and also according to J. C. 

 HOLM (II.) a few species of Schizosaccharomyces, one of which 

 perished within a year in saccharose solution, though found to be 

 still living in wort after two and a half years. Beer wort, on the 

 other hand, proved unreliable with all the others tested for this 

 purpose. True, in not a few instances, living cells were found in 

 it after ten or even eleven years, but just as frequently none could 

 be detected at the end of a single year. This liquid is subject to 

 considerable variations in constitution which caonot be influenced 

 or ascertained by the experimenter. In countries where the 

 summer is hot, provision must be made at that season for artifi- 

 cially cooling the cultures (in an ice-chest of special construction) ; 

 otherwise, as was observed by H. WILL (XIX.) in Munich, and by 

 A. KUKLA (I.) in Prague, degeneration and death will occur even 

 with saccharose solution. In consequence of unfavourable expe- 

 riences, A. JORGENSEN (IX.) recommends that streak cultures on 

 wort gelatin should not be employed for storage purposes. The 

 tendency to and results of the formation of films on ageing 

 cultures have been already referred to on p. 120, vol. ii. 



The colour of beer wort is ameliorated by the fermenting yeast, 

 not solely (as is known to every brewer) during primary fer- 

 mentation, but also, and to a far greater extent, when the fer- 

 mented beer is left for a long time in contact with the sedimental 

 yeast, as is the case when yeast cultures are stored in wort. A 

 gradual and extensive decoloration of the nutrient medium occurs 

 (see p. 126, vol. ii.) ; so much so, in fact, that the colour may be 

 changed from brown to pale straw-yellow. The experiments con- 

 ducted on this point by H. WILL (XXV. and XXII.) showed that 

 the wild yeasts generally are more powerful decolorants than the 

 culture yeasts. 



When a pure culture has to be transferred from one laboratory 

 to another, which possesses the necessary equipment for further 

 reproduction, a small quantity of the culture even a couple of 

 vigorous cells will suffice is placed on a little cotton-wool and 

 inserted in a previously sterilised Freudenreich or Freudenreich- 

 Hansen flask. The cotton should not have been freed from fat, 

 and will then be hygroscopic enough to supply the yeast with the 

 requisite minimum of moisture to prolong its vitality. The 

 Hansen modification of the Freudenreich flask (Fig. 162) differs 

 from the original type by the provision of a slanting tube at the 

 side to facilitate connection with a Pasteur flask, both for intro- 

 ducing a drop of the transferred culture on to the cotton (e) and 

 also for inoculating it into a fresh nutrient solution. A coating 



