34 PHYSICAL CHEMISTRY IN BIOLOGY. 



is not responsible for the permeability, but the outer layers of the muscle 

 protoplasm are. 



The skin of amphibians seems according to OVERTON to behave like the muscles * 

 in regard to permeability 



Theories of Admissibility. On what does the permeability or non- 

 permeability of cells for certain bodies depend? The discoverer of pre- 

 cipitation membranes, M. TRAUBE, considered the membrane as a sort of 

 molecular sieve. The relation of the size of the particles passing and 

 the width of the pores of the membrane was important. 2 



OVERTON states that " the reason of the very variable permeability 

 of living protoplasm, or better the plasma membrane for various com- 

 pounds, lies in an impregnation of the membrane by bodies of similar 

 solvent ability like the high molecular monatomic alcohols, ether, olive 

 oil, etc. All compounds which are readily soluble in this impregnable 

 substance pass quickly into the cell, while those compounds which are 

 considerably less soluble therein than in water pass more slowly into the 

 cell, and indeed the slower the more the distribution coefficient changes in 

 favor of the water (page 48). Those compounds which are practically 

 insoluble in the impregnable substance do not pass into the cell." 3 



Certain substances which are of the very greatest importance for 

 life processes and which probably are burnt to a great extent within the 

 cells, have, according to the above experiments, either no ability to 

 enter the cells, or only a limited ability. These bodies are the sugars 

 and the amino acids. Also the presence of salts within the cells is not 

 easily understood with the above theory. For this reason OVERTON 

 calls the above treated permeability (for which his theory attempts 

 an explanation) passive, and differentiates this from the active, in v which 

 the protoplasm of the cells are active in one unknown way or another. 4 



MOORE and ROAF believe that the salts exist in the blood corpuscles 

 in the form of " adsorpates." The cells therefore do not take up added 

 salts, because the absorbing proteins have reached their saturation limit 

 (p. 48) s 



Osmotic Pressure of Animal Fluids. As is apparent from the 

 above, a substance exerts upon living cells an entirely different influence, 

 depending upon whether the substance is able to pass into the cell or 

 not, or whether the substance which does not pass in has the ability 

 of attracting water or not. Therefore that part of the osmotic pres- 



1 Verhandl. d. phys. med. Gesellsch. zu Wiirzburg, (N. F.), 36, 277, 1904. 



2 Arch, f . Anat. Physiol. u. Med., 1867, 87. 



3 Vierteljahrsschr. d.'naturf. Gesellsch. zu Zurich, 44, 88, 1899, and Nagel's Hand- 

 buch d. Physiol. des Menschen. II, 817. 



4 Nagel's Handbuch d. Physiol. des Menschen. II, 816. 



5 Biochem. Journ., 3, 55, 1908. 



