THE PERMEABILITY OF CELLS 543 



excluded dust and prevented evaporation. The water was redis- 

 tilled in glass from KoMuoOs and NaOH and was non-toxic. 

 The first third of the distillate was rejected. 



Two different cultures of Paramoecia were used and they 

 showed characteristic differences, both as regards resistance to 

 the toxic effect of the alkali and rate of penetration of the alkali. 

 Different species of Protozoa show likewise quite different degrees 

 of resistance. An Oxytricha, Chilomonas and a Colpidium in- 

 troduced along with Paramoecium into certain of the alkaline 

 solutions appeared quite unaffected while the Paramoecia them- 

 selves were killed in a short time. 



The individuals used in experiments, the results of which are 

 given in table 6, were large and the amines and ammonias pene- 

 trated much less readily than in the second culture. The com- 

 parative differences between the alkalies are constant however. 



In every instance the last seven substances enter Paramoecium 

 readily and change the red dye to yellow; the first seven only 

 enter long after all motion has ceased, and the organism is very 

 much swollen and dead. If it burst or is crushed so that the 

 surface is ruptured the alkali enters at once and turns the neutral 

 red to yellow. Or if the animal's surface is changed by CHCI3 

 water or chloretone the alkali is found to enter immediately. 



A detailed comparison of the effects produced by NH4OH and 

 NaOH on stained Paramoecium will serve to make clear the 

 differences between the two groups of alkalies, as regards diffusi- 

 bility through cell membranes. The second culture of smaller 

 individuals was used in this comparison. 



1 o'Vo NH4OH — Paramoecia placed in this solution at first give the 

 avoiding reaction. The movement is immediately slowed and the 

 animals revolve slowly on their long axis first forward a short distance 

 then backward. Change in shape begins immediately, the twist of the 

 hind end becoming less marked. The change in color of neutral red also 

 begins immediately; the red gradually fades and the animals are color- 

 less in two to three minutes. Some individuals showed clear drops 

 (vesicles) along the sides of the body in about four minutes. These 

 individuals ceased movement in five minutes and disintegrated. The 

 remainder (about half) simply swell often with protrusion of the 



