1913.] A Study on the Action of Surface Tension. 



535 



probable that surface tension is the only immediate factor involved in this 

 condensation. Of these he has given an account in recently published 

 communications (10, 11, 12). 



More recently, however, the author has found a unicellular animal form, 

 in which the action of surface tension in influencing the distribution of salts 

 in it is, to all appearance, placed beyond doubt. 



This organism is Acineta tuberosa, a Suctorian Protozoan of marine habitat, 

 a form which permits readily of technical manipulation and microscopic 

 examination, especially for microchemical purposes. Some, at least, of the 

 salts of sea water penetrate its cytoplasm, and amongst these certainly are 

 those of potassium, of which the chloride is apparently the most abundant. 

 The distribution of this element in the cytoplasm of this organism was 

 carefully investigated, and the results were found to be of such significance 

 as to justify the detailed description of them given in the following pages. 



II. Methods of Investigation. 



The specimens of Acineta tuberosa used in these observations were found 

 in abundance attached to brown filamentous algae growing on wooden 

 wharves and floats, at and just below the surface of the water, near the 

 Marine Biological Station of the Biological Board of Canada, in the Bay of 

 St. Andrews, !New Brunswick, in July and August of 1911. It was easy at 

 any time during that period to get an abundant supply of these specimens 

 by collecting a mass of the algae, which was carried to the laboratory in a 

 quantity of the sea water of the immediate locality. In nearly all cases the 

 material so collected was used within a few minutes — 20 at the most — after 

 it was collected. 



For the determination of the distribution of potassium in the Acinetce, a 

 mass of the algae was lifted with a forceps from the sea water, and allowed 

 to drop into a quantity of the solution of the hexanitrite of cobalt and 

 sodium. For the method of preparing this reagent, the reader is referred to 

 an earlier article of the author's (9). At the end of five minutes the mass of 

 filaments was removed from the reagent and placed in ice-cold distilled 

 water, which was renewed every three to five minutes, until, at the end of 

 half-an-hour, all the uncombined reagent was completely extracted, and the 

 only demonstrable cobalt compound present was that in the form of the 

 triple salt, the hexanitrite of cobalt, potassium and sodium. The filamentous 

 mass was now placed in a quantity of a mixture constituted of equal parts 

 of glycerine and fresh or recently prepared ammonium sulphide, which gave 

 the preparation a black reaction, due to the formation of the black cobaltous 

 sulphide compound. 



