BOUNDARY LAYER OF CELLS. 21 



NERNST 1 has shown by a special experiment that the permeability 

 of a membrane for a certain substance is essentially dependent upon the 

 solvent power of the membrane for the said substance. This point, 

 which is of the greatest importance in the study of osmotic phenomena 

 in living cells, has been specially investigated by OvERTON. 2 The 

 behavior of the living cells toward dyestuffs, also the ready introduc- 

 tion into animal and plant protoplasm of such bodies as are insoluble 

 or only slightly soluble in water but readily soluble in fats or fat-like 

 bodied, has led OVERTON to conclude that the protoplasm-boundary 

 layer behaves like a substance layer whose solvent power is closely 

 related to the fatty oils. According to this investigator, the protoplasm- 

 boundary layer is probably impregnated with lipoids, i.e., bodies which 

 in regard to solubility and solvent power are more or less similar to the 

 fats. The lipoids are not a class of bodies that can be defined chemically. 

 The nature of certain of them is still not well known ; but the best-known 

 bodies, such as lecithin (the phosphatides especially) and cholesterin, 

 must be considered as of the greatest importance. 



The occurrence of an accumulation of lipoids as a special external 

 boundary layer in the cells is not a sufficiently proven fact,. and at least 

 does not apply to all animal cells, and is not necessarily important in the 

 explanation of the action of lipoids. Objections have also been made 

 by many investigators to OVERTON'S theory, which has received rather 

 general acceptation, 3 It does not apply to all cases ; for example, 

 according to COHNHEIM, it does not explain the absorption in the intestinal 

 canal, and according to MOORE and ROAF it does not explain certain prop- 

 erties of the cells, namely, the different composition of the electrolytes 

 within and without the cells and the selective taking up of certain 

 soluble substances, such as foodstuffs, therepeutic agents, toxines, and 

 antitoxines, on the part of the cells. The researches of these last investi- 

 gators are based essentially upon the behavior of mineral bodies, and they 

 show that the above theory presents certain difficulties in the understand- 

 ing of the very important exchange of mineral bodies between the cells 

 and the external fluid. 



This leads us to the question as to the importance of water and the 

 mineral bodies, which are of just as great moment for the life of the 

 cells and their metabolism as the organic constituents. In regard to 

 the water this follows from the fact that the animal body consists of 



1 Zeitschr. f. physikal. Chem., (>. 



2 Vierteljahrsschr. d. Naturf . Ges. in Zurich, 44 (1899), and Overton, Studien iiber 

 die Narkose, Jena, 1901. 



3 See O. Cohnheim, Die Physiologic der Verdauung u. Ernahrung, 1908. J. Loeb 

 in Oppenheimer's Handbuch der Biochem., 2, p. 105. T. B. Robertson, Journ. of BioL 

 Chem., 4, 1908; B. Moore and H. Roaf, Biochem. Journ., 3, 1908. 



