302 



Mr. S. G. Paine. 



[July 12, 



The ammonium sulphate was estimated in the initial and firfal liquids 

 only, the amount in the final yeast being found by difference. 



The results with ammonium sulphate are found to be very similar to those 

 obtained with sodium chloride. 



Experiments 145 and 151 are specially interesting as the initial yeast in 

 these cases contained a large percentage of solid matter. In the former, 

 where one-tenth molar ammonium sulphate was employed, 33 - l7 grm. of 

 water have entered the yeast while only 0-16 grm. of the salt have been 

 carried in, and in the latter from three-tenths molar solution 25"47 grm. of 

 water and - 52 grm. of salt have entered. The ratio of the concentration 

 inside the cells to the concentration outside is the same in both cases. 



The rate at which a sample of air-dried yeast will absorb water and recover 

 turgescence is very remarkable. In ~No. 145 when 30 grm. of the yeast were 

 mixed with 60 c.c. of solution such a stiff paste was obtained, within 

 two minutes, that it could only be stirred with difficulty. It is further 

 worthy of note that yeast which has been dried in air returns to its normal 

 condition of turgescence when immersed in water, as shown by the percentage 

 of total solids. In all samples of fresh pressed yeast the total solid content 

 has been found to vary from 28 to 35 per cent. Total solid estimations of 

 three air-dried samples gave 68"4, 50*5, and 37"5 per cent. ; when immersed 

 in water these yeasts became turgid with a normal solid content of 30 - 5, 

 31, and 32 - 4 per cent, respectively. 



The envelope of such dried and shrivelled cells, though readily permeable 

 by water, does not admit of the entrance of a 1/10 molar solution of 

 ammonium sulphate, but selects from it a large quantity of water and only 

 a relatively small quantity of the salt. The liquid surrounding the cells 

 therefore becomes considerably concentrated. In Experiment 145, for 

 instance, the concentrations of salt in the initial and final liquids were 

 1-26 and 1*66 respectively. 



Copper Sulphate. 



A peculiar resistance to the entrance of copper salts is exhibited by the 

 protoplasm of Penicillium glaucum (12), growth of which has been found 

 possible on a medium containing as much as 21 per cent, copper sulphate, 

 although very much smaller quantities down to 3 per cent, have occasionally 

 proved destructive. In view of this result it seemed advisable to investigate 

 the effect of solutions containing copper upon the protoplasm of the yeast- 

 cell. 100 grm. of yeast were suspended in 100 grm. 1/10 molar CUSO4, 

 allowed to stand for the usual time in the cold room, and the distribution 

 of the copper determined. 



