PHTSIOLOGT 37 



the sea water in respect to this gas, the concen- 

 tration inside is always less than outside (except 

 in quite acid solutions), and as the alkalinity of 

 the external solution increases, and the hydrogen 

 sulphide becomes more completely ionized, its 

 concentration in the sap becomes less. This is 

 shown in Fig. i, in which the concentration of 

 total hydrogen sulphide in the sap is designated 

 by the symbol (O) and the concentration of un- 

 dissociated hydrogen sulphide in the sea water 

 is designated by the symbol {^) when calculated 

 from the dissociation constant, by the symbol 

 (A) when determined by the method of vapor 

 tension, and by the symbol ( X ) when measured 

 by the rate of evaporation. 



Not only the inside concentration but also the 

 rate of penetration corresponds closely to the 

 concentration of undissociated substance outside. 

 This indicates that under normal conditions 

 hydrogen sulphide cannot enter the cell very 

 rapidly except in the form of undissociated 

 molecules and that it does not dissociate to any 

 great extent after entering the cell. Precisely 



