CONDITIONS OF CELL REPRODUCTION. 229 



ductive capacity is stated by R. PEDERSEN (II.) to be small. More 

 exhaustive experiments were instituted in 1887 byJ.ARCHLEB (I.), 

 pressed yeast (i grm. per litre) being treated with malt extract 

 ranging in strength from i to 25 per cent., the largest yeast crop 

 was furnished by the 14 per cent, solution. In the case of a 

 Burton yeast grown by A. J. BROWN (VII.) at 20 C. in hopped 

 ale worts of various strengths, gave no increase in crop when the 

 concentration exceeded about 15 per cent. Balling. A. L. STERN 

 (III.) who grew Burton yeast in two sets of experiments in which 

 the asparagin content (3 grms. and 1.5 grms. respectively) was 

 constant, whilst the dextrose varied between o and 30 per cent., 

 obtained the maximum yeast crop with 15 per cent, of sugar in 

 the one case and 12.5-15 per cent, in the other. Again, the 

 experiments of EMIL BAUER (III.) show that any excess of nitro- 

 genous nutriment (whether in the form of yeast extract or of the 

 autodigestion products of yeast) beyond the amount absolutely 

 necessary has no influence on the crop. 



Nutrient solutions which are very rich in sugar, and therefore 

 have a strongly plasmolytic action on the cells, retard or even 

 entirely prevent reproduction, a circumstance that is utilised in 

 cookery for the preservation of fruit. No generally applicable 

 data can be given respecting the proportion of sugar necessary 

 to cause plasmolysis, because the corresponding influence of other 

 ingredients in the solution also comes into play. In the experi- 

 ments of E. LAURENT (VI.) with a number of beer and wine 

 yeasts, the appreciable reproduction ceased in the cultures in 

 which the nutrient solution (a decoction of malt culms) contained 

 about 60 grms. of saccharose, invert sugar, dextrose or maltose 

 per 100 c.c. Greater powers of resistance in this respect are pos- 

 sessed bySacch.Zopjti; and the yeast isolated by E. DUBOURG (II.) 

 from sweet Sauterne proved capaple of acting in an 80 per cent, 

 solution of invert sugar. A. MAYER (VI.) claimed that the plas- 

 molytic action of a 30 per cent, sugar solution could be counter- 

 acted by a small percentage of Seignette salt, the addition of which 

 soon caused abundant reproduction and powerful fermentation in 

 a previously quiescent nutrient medium ; but this was disproved 

 by M. HAYDUCK and M. DELBRUCK (I.). Greater powers of with- 

 standing the influence of high percentages of sugar and other 

 ingredients in the nutrient medium are possessed by the yeasts 

 concerned in the (spontaneous) fermentation of Danzig Jopen 

 beer (chiefly exported to England, under the name spruce beer or 

 black beer). This was demonstrated by P. LINDNER (XIV.), who 

 isolated two new species of yeast, tiacch. farinosus and Sacch. 

 Sailiij from fermenting Jopen wort of the initial concentration 

 53-54 per cent. Balling. 



The relative permeability of the cell membrane also affects the 

 reproductive power. This permeability varies, not merely in the 

 different races of yeast, but among individuals of the same race, 



