268 HEREDITY IN SACCHAROMYCETES. 



from practical sources, on the variation known as degeneration in 

 pitching yeast, will be found in the columns of the technical press 

 for some years past ; and we will now merely cite two communi- 

 cations relating to injurious variations. One cause of yeast 

 degeneration is ascribed by HAYDUCK (VI.) to the enrichment of 

 the yeast with nitrogen, and he recommends, as a means of 

 regeneration, that the yeast should be allowed to ferment a solu- 

 tion of saccharose before pitching. In the case of a yeast which 

 suddenly began to clarify badly, SEYFFERT (II.) found that the 

 addition of gypsum to the brewing liquor (well water) restored 

 matters to their normal condition. Sudden disagreeable changes 

 with regard to smell and flavour may also arise in practice, the 

 cause being generally attributed to cultivation at abnormally high 

 temperature, excessive rousing of the wort, &c. ; and WILL (XXIX.) 

 states that boiling the wort too long in the steriliser may also 

 influence the activity of the yeast. In short, the yeast may 

 be affected by any unusual conditions in brewing ; and in this 

 category should be included the experiments of Biernacki, Effront, 

 Hayduck, Heinzelmann and Schulz, with chemical stimulants (see 

 vol. i. p. 1 08). In addition to Hansen, observations on the 

 variation of pitching yeast in practice have also been published 

 by Delbriick, A. Jorgensen, Kukla and Will. 



Proof of the temporary character of the variations caused in 

 practice by the influence of the conditions prevailing there is 

 afforded by the fact that the pure-culture system has not only 

 obtained a solid footing in breweries throughout the world, but is 

 also gaining ground daily in other fermentation industries. 

 Certain culture yeasts are particularly constant, others again show 

 a tendency towards variation. Carlsberg bottom yeast No. i 

 belongs to the former class, a pure culture of this yeast having 

 retained its character, apart from temporary fluctuations, for more 

 than five years in the fermentation cylinder of the pure-culture 

 apparatus at the New Carlsberg brewery. Various authors have 

 reported on special constancy in culture yeasts, the researches of 

 Irmisch, A. Jorgensen and P. Lindner being worthy of note in this 

 connection . 



As we have seen, the practical application of the pure-culture 

 system consists not merely in the preparation of pure cultures of 

 a given species or race, but also in a selection of the vegetations 

 furnished by individual cells. In this way the introduction of 

 pure cultures in the brewery is accompanied by an attempt at race 

 improvement, the requirements being confined not merely to the 

 preservation, by the race or species, of all its properties that are of 

 value to the brewery, but extending to the selection of individuals 

 exhibiting variations of special value for the brewery in question 

 that is to say, possessing the good properties in an increased 

 degree and with the undesirable qualities eliminated. Of course 

 these results cannot be more than partially accomplished even in 



