534 EDMUND NEWTON HARVEY 



entrance of a concentration of OH ions sufficient to affect the 

 neutral red combination. In the case of the inorganic alkahes 

 and N(C2H5)40H death is to be referred to two possible causes. 



First, and of greatest importance, the alkali only enters after 

 the cell surface has been destroyed. This is best illustrated by 

 comparison of the mode of entrance of NH4OH and NaOH into 

 Paramoecium (p. 546) and is strong evidence in support of Hoeber's 

 ('06, pp. 260, 266-267) theory that the strong electrolytes, in 

 general, produce their effects by a change in the colloids of the 

 cell surface and not of the cell interior. 



Second, the combination of the strong alkalies with the cell 

 surface proteids may be irreversible, whereas the combination of 

 the weak ammonia is easily reversible. 



The cell surface of the living as compared with the dead (by 

 chloroform treatment) cells offers a highly resistant barrier to 

 the entrance of the strong alkalies but both living and dead cells 

 are almost equally permeable for the weak alkalies (see table 4). 

 This suggests, but does not prove, that if small quantities of 

 NaOH could enter without affecting the membrane, the cell 

 would be as unharmed as in NH4OH. 



Ammonia has likewise a toxic effect but it is only manifest after 

 a longer exposure, and is quite independent of the entrance o^ 

 ammonia into the cell. Red Elodea leaves recover if placed in 

 fresh water immediately after decolorization in ^ NH4OH. If 

 left for five minutes the dye becomes red again but the cells 

 eventually die. If left over 30 minutes even the red color fails 

 to return. The leaf is of course killed. 



The inorganic hydroxides (and N(C2H5)40H) only enter the 

 cell after they have affected the normal impermeability — in other 

 words after they have rendered its surface permeable to them- 

 selves. It seems best, then, to speak of a resistance of the cells 

 for the strong and a permeability of the cell for the weak alkalies. 



Reversibility of the neutral red color change is quite indepen- 

 dent of the death of the cell. The red returns after decoloriza- 

 tion by the amines although they produce fatal after-effects. 



It likewise returns in cells first decolorized in ammonia and then 

 killed with chloroform water, and more rapidly than in the 



