1913.] 



A Study on the Action of Surface Tension. 



547 



van 't Hoff-Arrhenius theory of osmosis based on the results of the experiments 

 of de Vries and Pfeffer. This compels a revision not only of the doctrine of 

 the semi-permeable membrane as applied in physiology but also of not a few 

 of the conclusions that were based on it. 



V. Summary of Results and General Observations. 



1. In Acineta tuberosa, a marine Suctorian Protozoan, the potassium salts 

 are localised : (1) On the interface between the cytoplasm and each of the 

 spherules strewn throughout the cytoplasm ; (2) on the cytoplasm-germ-bud 

 interface ; (3) in the superficial film of each extended tentacle. 



2. The quantity of potassium found at each cytoplasm-spherule interface is 

 generally very minute, and may be observed only after careful examination 

 in some preparations ; the quantity on the cytoplasm-germ-bud interface is 

 usually richer and more readily demonstrable ; while the potassium is most 

 abundant in the surface film of each extended tentacle. 



3. The potassium in the remainder of the cytoplasm does not give a reaction 

 with the reagent used, the hexanitrite of cobalt and sodium. With this 

 reagent crystals of the triple salt, the hexanitrite of cobalt, sodium and 

 potassium, may be formed in solutions as dilute as 1 of potassium in 275,000, 

 but in microscopical preparations of cells appropriately treated with the 

 reagent and subsequently with ammonium sulphide the sensitiveness of 

 the reaction exceeds that limit, perhaps to the extent of demonstrating 1 

 part of potassium in 1,000,000. In any case the absence of a reaction in 

 the cytoplasm generally is an indication that the potassium salt or salts 

 present are in exceedingly attenuated dilution. 



4. When the tentacles begin to retract, the potassium salt or salts in the 

 film of each begins to diffuse into the cytoplasm of the main body of the 

 organism. This diffusion results in a greater concentration at first in the 

 cytoplasm near the base of the hillocks from which the tentacles take 

 their origin, but, as the retraction proceeds, the diffusion progresses down- 

 ward into the cytoplasm, which is now more or less deeply impregnated 

 with potassium salts and the deposit on each cytoplasm-spherule interface 

 becomes, as a rule, more distinct. 



5. Complete retraction of the tentacles alone is rarely seen, but more often, 

 though never frequently, one finds a complete retraction of hillocks into 

 which the tentacles have been completely withdrawn. In the masses 

 derived by retraction of such hillocks the potassium salt is still present, 

 but a distinct reaction for potassium in the underlying cytoplasm shows 

 that diffusion of potassium into the cytoplasm, as a result of the retraction, 

 has proceeded. 



