546 



Prof. A. B. Macallum. Acineta tuberosa : [Feb. 19, 



that in such growing structures they may play, amongst other parts, that one 

 of lowering the surface tension at points on the cells where extensions of the 

 latter occur. As there is not a great gulf fixed between the metabolism of an 

 active vegetable cell and that of a vigorous animal cell the existence in the 

 latter of free amino-acids on occasions is not improbable. 



The observations just now advanced are, of course, largely of the order of 

 speculation. They have been put forward because they are in a measure 

 concerned with another problem for which the lipoid theory of membrane 

 action has been proposed as a solution. 



With a concentration of potassium in the superficial molecular layer of each 

 tentacle giving a precipitate much denser than sea water gives with the 

 hexanitrite reagent, the question arises why the potassium salt in the surface 

 film of each tentacle does not diffuse into the sea water and equalise the con- 

 centration on both sides of the tentacle-sea- water interface. The presence of 

 a lipoid in the superficial film would perhaps account for this inequality, for 

 the lipoid would make the membrane more or less impermeable, not only to 

 water but also to salts in the latter. This, however, does not aid much in 

 the way of explanation, for if the superficial film owes its impermeability to a 

 lipoid constituent there should be no penetration of the superficial film by a 

 solution of a potassium salt from the cytoplasm underneath and no con- 

 densation of potassium would occur in the film. It is obvious, therefore, 

 that the impermeability of the superficial layer of protoplasm of the tentacles 

 cannot be due to a lipoid and that some other factor plays the important part. 

 That force is surface tension, in all probability, for the force that condenses 

 the potassium salt in the superficial film of each tentacle would hold it there, 

 especially as the surface tension of the sea water is higher than that of 

 cytoplasm and a diffusion of potassium salt into the sea water would tend to 

 raise the tension of the latter, thus increasing, instead of decreasing, the 

 inequality of the forces on both sides of the membrane-sea-water interface. 

 If the surface tension of the external medium were equal to, or lower than, 

 that of the superficial film of the cytoplasm of the tentacles, diffusion outward 

 would take place in order to equalise the tensions on the two sides of the 

 dividing interface. In support of this it may be pointed out that Czapek (2) 

 has found that it is only when the external medium of vegetable cells has its 

 surface tension lowered to - 68 times that of pure water that the tannin 

 diffuses from them into the external fluid. 



Besides the influence that surface tension has upon the distribution of salts 

 in the interior of living cells it has, it would appear, a very important effect 

 upon the diffusion from them and, therefore, into them. The factors operating 

 in cellular osmosis are, consequently, not so simple as those postulated in the 



