472 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



.00700 ra. CaClj. 



Time lir. 22 hr. 49 hr. 



No. of Stentors 100 115 109 



No. of Divisions .... 15 15 



Mortality 6 



Mean Result 1.15 1.09 



Control. 



(Culture medium No. 20318.) 



Time hr. 26 hr. 



No. of Stentors 100 127 



No. of Divisions 27 



Mortality 



IMean Result 1.27 



The results of the experiments thus far described and plotted in the 

 accompanying curves (p. 473) permit some inference as to the relative 

 vaaomtndie of \.\\e factor of molecular concentration, and to this subject I 

 shall recur in detail later. To get an independent estimate of the osmotic 

 factor, I determined to make some experiments in which this should be 

 the principal factor involved. Some trials were made with cane sugar, 

 but the samples used were probably contaminated and not sufficiently 

 recrystallized. However, the most serious objection to this substance, 

 for my purpose, was its strong tendency to acid fermentation. The 

 presence of acid occurs so soon after the solution is made as to become 

 an important factor in results taken after twenty-four to forty-eight hours 

 or more. After several trials the use of cane sugar was abandoned. 

 Fortunately milk sugar proved to be practically innocuous to Stentor, 

 and it lias the advantage over cane sugar that its fermentation is very 

 slow. Tolerably pure samples were purchased and freed from dust and 

 other contaminations by repeated crystallization from hot solution. Par- 

 allel with the application of milk sugar I applied to Stentor of the same 

 origin a concentration of 0.00700 m. sodic chloride, sufficient, according 

 to previous experience, to produce a marked effect. I selected sodic 

 chloride for comparison because of its want of any marked siiecific effect 

 upon division (cf. potassic chloride). The osmotic concentration of a 

 0.00700 m. sodic chloride solution is about equivalent to that of a 0.01250 m. 

 milk-sugar solution, and this latter is the lowest concentration of milk 

 sugar u^ed in this experiment. For comparison with the salts, the 

 a[)plication of a substance (milk sugar) found to have practically no other 



