RESEARCHES ON YEASl^S. 99 



upon yeast cells in such a way that they can be made to 

 impart to fermenting liquids a taste and odour different from 

 that originally characteristic of the yeast. Experiments in 

 this direction may acquire practical importance especially in 

 the manufacture of wine. 



Most of the changes mentioned above are of a somewhat 

 temporary character. A more deeply seated change, and 

 one of greater permanency was attained in the case of the 

 species which I have named, Sacch. Ludwigii (' Centralblatt 

 f. Bakteriologie und Parasitenkunde,' 1889, p. 632; ' Zeitschr. 

 f. d. ges. Brauw.' 1889, p. 253). By the systematic selection 

 of single cells, and cultivating each separately, I succeeded 

 in obtaining three different forms of growth of this species. 

 When these were cultivated separately in wort, and tested 

 for spore-formation in the ordinary manner, it was found 

 that one variety yielded spores abundantly, the second only 

 very sparingly, whilst the third gave no spores.* Numerous 

 generations of this last form were cultivated in wort both 

 at the ordinary room-temperature and at 25 C., and under 

 conditions of nutriment which ordinarily favour the spore- 

 forming power of a yeast, but it still refused to yield spores 

 either on moist gelatine or on moist gypsum blocks. Only 

 after the cultivation in wort had been continued for a length 

 of time were growths gradually obtained which again yielded 

 spores, and then never in abundance. If, on the other hand, 

 the cultivation were made in a 10 per cent, solution of dex- 

 trose in yeast water, new generations were at once obtained, 

 whose cells again possessed the property of yielding spores 

 in abundance. In order to bring back the cells to their 

 normal function, the new nutritive liquid was required. 



We will now consider some cases in which the change is per- 

 manent, and repeats itself again and again in new generations. 

 In the treatise quoted above, I gave an account of the main 

 results of my experiments on Sacch. Pastorianus I. It was 

 found that when the cells of this species were cultivated for a 



* I have obtained similar results also with brewery yeasts. 



H 2 



