TENSION PHENOMENA OF LIVING ELEMENTS. ll"J 



or with cell sap. He supposed these membranes to be the semi- 

 permeable parts of the cell, and that they became altered at 

 death. Pfeffcr called this membrane on the cell surface the 

 "plasma membrane." 



Whereas the nuclear membrane and certain vacuole mem- 

 branes are semipermeable, these are lacking in crythrocytes, 

 which arc then-fore good objects for testing the question whether 

 the protoplasm in general, or merely its surface, is semipermeal >le. 

 Hober 1 by two very ingenious but complicated methods, one 

 based on dielectric capacity, determined the electric conduc- 

 ti\it\ <>f the interior of the erythrocyte without rupture of the 

 pl.i-nia membrane. Since the conductivity of the interior 

 'about that of a .2 per cent. XaCl solution) was found to be 

 ni.mv times greater than that of the erythrocyte as a whole, the 

 membrane must be relatively impermeable to ions. There is 

 much other, but less direct, evidence that the semipermeability 

 resides in the plasma membrane, namely: the rapidity of change 

 in permeability of certain cells, the sudden innva-e in perme- 

 ability of a cell after swelling to a certain size idue presumably to 

 rupture of the plasma membrane), the ease with which mild 

 mechanical treatment increases the permeability, and the locali- 

 /ation of electric polarization at the cell surf 



< Miim k -upposed these membranes to be of a fatty nature. 

 This idea \\as carried further by Overtoil, who considered the 

 plasma membrane to be composed, not of neutral lai-, but of 

 sub- 1. in. es of the class which are called "lipoids." \\ hich included 

 iion--aponif\ ing ether soluble extracts of or-an-, /. <-., choN-tcrm, 

 lecithin, cuofin, and rerebrin. He found 3 that all basic dyes 

 were ea-ilv absorbed by living cell.-, but not mo-i of the -ulphonic 

 acid dyes. This corresponded to their -olubility in melted 

 cholesterin. or solutions of lecithin and cholesterin, or particles 

 of lecithin, protagon or cerebrin. His argument is somewhat 

 \\eakened. hou ever, by the fact that cholesterin decomposes 

 on melting, and that if lecithin is allotted to absorb water its 

 s. .1\ cut potter changes. 



\rtlt. f. .: /., 1910, CXXXIII., 237, and Eighth Internat. I'hysiol. 



I'mmif . Vi.-mui. H)IO. 



her. (/. Kn. Pm f. Akad. d. H U l'-rlin, 1888. B<1. XXXIN". 



*Jahrh . Bo/., ij->n. X X X l\ . 669. 



