RESISTANCE TO HYPOTONIC SEA-WATER 233 



have been in part due to the action of bacteria, although this is 

 practically ruled out in those experiments in which the solution was 

 given a fair pasteurizing treatment in the formation of the extract, 

 which was later boiled vigorously. The bacterial growth in such 

 solutions must have been slight, at least in the early history of the 

 isolations. 



With the Paramecium culture medium the role played by the 

 different elements entering into the conditioning of this medium 

 could be told only by experimentation. The Paramecia were grow- 

 ing in a hay infusion which contained the water extracts of the hay 

 as well as the products of bacteria and of Protozoa other than the 

 Paramecia. All these must be considered as possible conditioning 

 factors, since the work above has clearly shown that the protection 

 is furnished by heterotypic as well as by homotypic conditioning. 



It has been possible to begin experimental analysis of the factors 

 leading to increased survival in these biologically conditioned solu- 

 tions. To date these indicate that the results are not primarily due 

 to the depressing action of the conditioned medium, in so far as 

 these are mimicked by dilute alcohol. They are not due to differ- 

 ences in pH. Gelatine suspensions do not confer similar benefits. 

 The colloids present do not mask the amount of electrolytes in 

 solution. 



Preliminary tests have been run to determine whether the protec- 

 tive substance would be adsorbed on animal charcoal. These gave 

 results of sufficient interest to deserve being presented in outline. 

 Animal charcoal was added to the dialyzed culture medium. The 

 whole was stirred, boiled, filtered twice with suction and once with- 

 out, and, after redialysis to 6,050 ohms, a standard survival experi- 

 ment was set up with hypotonic sea-water controls at 6,050 ohms 

 and 5,050 ohms. The resistance decreased in all solutions, as usual, 

 during the progress of the experiment. The solutions were changed 

 twice in the first 20 hours. As usual after standing, the culture water 

 had less electrolytes than did either of the accompanying solutions. 



Under these conditions the 50 Procerodes isolated into the treated 

 culture medium lived a mean time of 11.03 hours, while those in 

 hypotonic sea-water with the same initial resistivity lived 9.21 hours. 



