PHTSIOLOGT 27 



ported by the fact that the temperature coeffi- 

 cient is high. 



On the other hand it may be assumed that 

 the dye enters as a free base which dissociates 

 more in the acid cell sap than in the more alka- 

 line external solution and so accumulates in the 

 fashion discussed later on in connection with the 

 penetration of hydrogen sulphide into Valonia. 



Of especial interest is the fact that as the alka- 

 linity of the external dye solution increases the 

 rate of penetration increases and the excess of 

 concentration of the dye inside over that outside 

 also increases. This indicates that the penetrating 

 substance is the free base of the dye whose con- 

 centration would wax with increasing alkalinity. 

 This idea is also in harmony with the experi- 

 ments on exosmosis which show that when a 

 stained cell is placed in a solution destitute of 

 dye, the dye comes out more rapidly the 

 greater the acidity of the external solution. We 

 might explain this by saying that as the free 

 base comes out of the cell the concentration 

 gradient is greatly increased if the free base 

 is at once changed into another form 3 this would 



