1896.] MICROSCOPICAL JOURNAL. 281 



freeze a sample of yeast in Pasteur's solution, then thaw 

 out gently and slowly raise to 32 C. and cultivate it for 

 eight hours, after which determine the effects of freezing, 

 first whether fatal, second whether harmful at all. 



28. Light vs. Darkness. — Cultivate at 32° C. in Pas- 

 teur's solution, two lots of yeast, one in a closed oven from 

 access to the light, the other in the light ; after cultiva- 

 tion of 8-12 hours, study and determine whether light 

 plays any perceptible part in the cell life of the yeast cell. 



29. Effects of drugs — This study has for its object 

 to determine whether the presence of minute traces of 

 various drugs affect cell life, and .whether some drugs 

 are more powerful than others. The method is to add 

 to an optimal culture varied amounts of these drugs and 

 then after several hours of cultivation to study their ef- 

 fects. A control culture must in each case be made for 

 comparison, in which none of the drug is placed. Any . 

 or all of the following are suggested: 



(a) Corrosive sublimate in distilled water. Yeast in 

 Pasteur's solution in following ratios, viz.: — (1) I : 5000 ; 

 (2) 1 : 10000 ; (3) 1 : 15000 ; (4) 1 : 20000 ; (5) 1 : 50000. 

 Determine whether yeast is able to live in any of these, 

 also whether it is killed instantly or after initial steps of 

 growth have taken place. 



(b) Carbolic acid in Pasteur's solution with yeast, 

 determine effects of following ratios, viz.: (1) 1 : 5000; (2) 

 1 : 2000 ; (3) 1 : 1000 ; (4) 1 : 500. 



(c) Alcohol— (1) 1: 100; (2) 5: 100; (3) 10: 100; (4) 

 20: 100. 



(d) Problems. Determine the ratio of different drugs 

 and compare with the above, testing to find the amount 

 the presence of which will arrest the growth or activity 

 of the cell. Some or all of the following can be used, 

 Prussic acid ; Arsenic ; Oil of Cloves. 



30. Vitality. — Cultivate under optimal conditions a 



