GENERAL PHYSICAL CONSTITUTION OF LIVING MATTER 45 



bring about a cataphoresis of the water or the particles dissolved in it, 

 into or out of the cell. 



But in view of the observations of MacCallum I am more inclined 

 to believe that contractile phenomena inside the cell furnish at 

 least part of the energy of secretion and absorption in those cases 

 where the osmotic forces alone cannot explain these phenomena. To 

 illustrate what possible form these forces may assume, I may point 

 out the rhythmical squeezing out of the liquid contents of the 

 vacuole in Infusorians. Here the work of secretion is obviously 

 done by protoplasmic contraction, and not by osmotic pressure. It 

 is quite possible that, mutatis mutandis, something similar may occur 

 in all cells, although this is only a surmise. 



6. FURTHER LIMITATIONS OF TRAUBE'S THEORY OF SEMIPERMEABILITY 



Traube's idea that all living cells are surrounded by a membrane 

 which is absolutely permeable for water, does not seem correct for a 

 number of marine animals. Fundulus heteroclitus, a marine fish, 

 lives and develops exclusively in sea-water, i.e. in a solution whose 

 osmotic pressure is, roughly estimated, like that of a half-grammolecular 



/f}'l\ 



( -- } solution of NaCl. I have found that this fish as well as its eggs 



can be put permanently into distilled water without the least injury. 

 No swelling of the eggs or the tissues occurs under these conditions.* 

 It may also be put into sea water whose osmotic pressure has been 

 increased by the addition of a certain percentage of NaCl without 

 perceptible shrinkage. This shows that water does not diffuse rapidly 

 through the skin of the animal or the membrane of the egg. It cannot 

 be stated, however, that it does not diffuse at all, since it is possible 

 that a slight diffusion of water into the cells may be compensated by 

 an increased secretion of water from the cells. In addition, the egg and 

 animal must be but slighly permeable for salts, as otherwise the salts 

 would diffuse from the blood and the tissues of the animal into the 

 distilled water, and this would cause the death of the animal. The 

 skin and the egg cannot be said to be absolutely impermeable, since gases 

 like O and CO 2 diffuse into the eggs, and since the latter rapidly dry 

 out and die when taken out of the water and exposed to dry air. More- 

 over, K and other toxic salts are able to diffuse slowly into the egg, as 

 can be shown by the fact that if potassium salts are added to sea water, 

 the heart of the embryo soon stops beating. 



* Loeb, Ffliiger's Archiv, Vol. 55, p. 530, 1893. Am. Jour. Physiology, Vol. 3, pp. 

 327 and 383, 1900 ; and Vol. 6, p. 411, 1902. 



