252 



MORRIS M. WELLS. 



TABLE V. 



SHOWING THE RESISTANCE OF AMPHIPODS IN DISTILLED WATER, WHEN EQUAL 

 NUMBERS OF ANIMALS ARE PLACED IN DIFFERENT VOLUMES OF WATER, OR 

 WHEN DIFFERENT NUMBERS OF ANIMALS ARE PLACED IN EQUAL VOLUMES OF 

 WATER (COMPILED FROM BULLOT, '04, PP. 204-5). 



Per Cent, of Animals Alive After 2 Days. 



Time Required to Kill One Half the Animals. 



In considering the possible importance of CO* as a factor in 

 the toxicity of distilled water, Bullot states that the water which 

 he used was very faintly acid to phenolphthalein, but not enough 

 to injure the animals. He says: "We know from the works of 

 P. Bert that, for cold-blooded animals like the frog, for instance, 

 CC>2 is toxic only when its concentration in the air reaches 15 per 

 cent. This corresponds to a solution of 15 per cent, of this gas 

 by volume, as the water dissolves its own volume of COo at 

 ordinary temperature and normal pressure. This quantity is 

 350 times larger than the one which could be found in the dis- 

 tilled water." A 15 per cent, solution of CO 2 means 150 c.c. 

 per liter of water. 1/350 of this is .42 c.c. In other words the 

 distilled water used by Bullot was practically neutral, since the 

 amount of hydrogen ion to be obtained from so small a quantity 

 of so little ionized an acid as carbonic acid, would be almost 

 negligible. In the gradient experiments cited in this paper, I 

 have shown that certain fishes are negative to so small a con- 

 centration of CC>2 as i c.c. per liter, in preference for slightly 

 higher concentrations. I have further shown that these fishes 

 do not live as well in distilled water that is practically neutral, 

 as they do in the same water made slightly (.00005 N) acid. 

 Thus the existence of a hydrogen ion concentration optimum 

 for these forms seems to be clearly demonstrated. 



