1913.] 



A Study on the Action of Surface Tension. 



545 



soaps, or certain lecithins, which may be present in the membrane of each 

 tentacle. The application, however, of a solution of osmic acid of 05-per- 

 cent, strength to living examples of Acineta has failed to give any indication 

 of the presence of these lipoids, while it demonstrated by a black reaction the 

 minute spherules of fat revealed by the scarlet red. 



There, consequently, appears to be little direct evidence that the low 

 surface tension of the tentacles is due to the presence of fat. It may, 

 indeed, be held that the presence of minute spherules of fat in their 

 membranes predicates a saturation of the latter with fat, which, however, is 

 so scanty that scarlet red and osmic acid fail to demonstrate it. If that 

 were the case it would be difficult to explain why the saturation did not 

 prevail over the whole surface of each hillock instead of being localised 

 as it is. 



The presence of minute spherules and other deposits of fat in the tentacles 

 may be the result and not the cause of the low surface tension in the 

 tentacles. Fats lower surface tension, it is true, but if the surface tension 

 should, through the action of some non-lipoid substance, be diminished, the 

 lipoid material, it is presumed, may condense where the tension is low and 

 give appearances in the tentacles like those described. 



The view that the tentacles of Acineta are hollow tubes open at their 

 capitate ends finds no support in the observations of the author, and it 

 follows that the food matter absorbed from the prey of these forms is not 

 taken into the cytoplasm of the tentacles unchanged or absorbed indis- 

 criminately by them. The homogeneous appearance of the axial portion of 

 each tentacle while it is attached to the prey suggests that the material 

 which is being taken into each tentacle is in a digested condition and that 

 the digestion so effected occurs outside the tentacles or in the interior of the 

 capitate ends. This involves the assumption that the tentacles secrete one 

 or more ferments. Now, the existence of proteolytic ferments in the 

 tentacles, even in minute quantities, would render the presence of amino- 

 acids possible and these latter would bring about a diminution of surface 

 tension which would maintain, if not originate, the extension of the tentacles. 

 These ferments would be more abundant, in the state of hunger, and specially 

 at the points where they would come most into service, and their activity, 

 however slight, directed upon the proteins at points in the hillocks, would 

 cause the protrusion of the tentacles there. 



The presence of free amino-acids in living protoplasm is not unknown and 

 especially in structures in which cellular activity is marked. In the growing 

 points of vegetable structures free amino-acids have been found in quantities 

 sufficient to render the demonstration of their presence certain. It is possible 



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