498 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



The results of the experiment show (1) the excellent adjustment of 

 Stentor to the four-salt mixture ; (2) the superiority of this combination 

 to any of its constituents used singly, it being double that of the meta- 

 bolic pitch indicated by calcic chloride. 



From the preceding experiments taken together inference of consider- 

 able reliability can be drawn as to the relative importance, or share of 

 activity, of each of the constituents. The result of making partial combi- 

 nations like the mixture of magnesic sulphate with sodic nitrate, as shown 

 above, gives information on this point, aiid this method is further applied 

 in the following final experiment. 



Expt., Feb. 6, 1903. 



The results show, as before, the excellent adjustment of Stentor to the 

 four-salt medium. They further show that the adjustment to two-salt 

 media is best with calcic chloride -f di-potassic phosphate ; but it is also 

 evident that the other constituents aided in producing the still better 

 result of the four-salt medium. 



I have used the above four-salt medium successfully for the estab- 

 lishment of mass-cultures. In such cases, owing to the addition of dry 

 leaves or reeds for food, I have doubled or trebled the proportions in 

 one hundred thousand, in order to overbalance the unknown salts intro- 

 duced by the food material. 



