1917] Mitra: Toxic and Antagonistic Effects of Salts on Wine Yeast 67 



ammonium phosphate that eventually formed furnished both the 

 nitrogen and phosphorus needed by the yeast. As yeast cells grow 

 easily in moderately acid, but not in alkaline solutions, the syrup 

 was left slightly acid, being tested by titration with N/10 solution of 

 sodium hydroxide. To facilitate the work, the syrup was boiled down 

 to 65 "Balling and put into a corked bottle. From this concentrated 

 synthetic solution a measured quantity was drawn off and diluted with 

 distilled water to 5°Bal. for use in the cultures. 



Method of Determining the Activity of the Yeast. — The experi- 

 ments were carried on in a series of 200 c.c. Erlenmyer flasks. To 

 each flask the weighed amount of salt was added and 100 c.c. of the 

 diluted synthetic solution placed in the flask by means of a 100 c.c. 

 pipette. 



The salts were weighed according to their respective molecular 

 concentrations. The flasks as soon as filled were plugged with cotton 

 and sterilized. After they had cooled down to the room temperature 

 they were inoculated with the yeast from a new culture. For this 

 purpose the new culture was prepared in a 200 c.c. Erlenmyer flask 

 containing 100 c.c. of the synthetic solution. The yeast thus became 

 habituated to this solution and therefore grew rapidly and uniformly 

 in the flasks. The new culture was transferred from a mother culture 

 in grape juice and put into the incubator for forty-eight hours at 

 28° C. At the end of this period the flasks containing the salts were 

 inoculated with one cubic centimeter of the new culture. After 

 inoculation, the flasks were put into the incubator, which was kept 

 at an approximately even temperature of 28° C. during the entire 

 experiment. 



As the alcoholic fermentation in the synthetic solution was not 

 rapid enough to serve as a criterion, the multiplication of the cells 

 was taken as the measure of the activity of the yeast. Accordingly 

 a microscopical count was made every forty-eight hours with a cali- 

 brated microscope. Five counts were made in each experiment, during 

 a period of about twelve days. In every case two blanks, with no 

 added salts, were made up, and the tables given represent the average 

 of two sets of duplicate experiments, except in the cases of potassium 

 chloride and magnesium chloride, where the results were so close that 

 only the first set of duplicates was used. It may be added that the 

 incubator did not keep exactly the same temperature throughout the 

 experiments, but ranged from 27°C. to 29°C. This difference of 2°C, 

 however, did not interfere appreciably with the uniformity of growth 



