REACTION AND RESISTANCE OF FISHES. 25! 



son, and Bottazzi (see pp. 279-280). The lowest concentration 

 which Jerusalem and Starling used was 2 per cent, of an atmos- 

 phere or about 20 c.c. CO 2 per liter. Their highest ran up to 

 200 c.c. per liter. Hooker ('12) tested the effect of carbon 

 dioxide upon muscular tone and, in opposition to Jerusalem and 

 Starling, concluded that this gas does not appear to be directly 

 beneficial to tissues, except in case of intestinal muscle rhythm. 

 He thinks it may be indirectly beneficial. Like most other 

 workers upon this problem, Hooker used very high concentra- 

 tions of the gas. His concentrations varied from 5 per cent, to 

 20 per cent, of the gas, in the atmosphere to which the solution 

 bathing the tissue was exposed. Water will dissolve nearly 

 its own volume of CQ 2 and thus the concentration of carbonic 

 acid varied from 50 to 200 c.c. of CO 2 per liter. The smallest 

 concentration used would kill most fresh-water fishes in a short 

 time. 



Reuss ('10) worked upon the effect of CO 2 upon the respira- 

 tion of fishes and concluded that it is an important one. The 

 regulation according to him is through the respiratory center 

 and not peripheral as Bethe ('03) believed. Shelford and 

 Allee ('130) note the extreme sensitiveness of fishes to COo in 

 gradients, and think the production of the gas as a product of 

 the metabolism of the organism may tend to increase its ex- 

 ternal effect when the fishes come in contact with water con- 

 taining it. 



Bullot ('04) in his work with the fresh-water amphipod (Gam- 

 marus) noted, as did Ringer in the case of fishes, that the animals 

 lived longer in distilled water when a number was present in a 

 given volume, or in other words, when the volume of water per 

 individual was small. He says: "If the amount of water 

 falls below a certain limit, the animals will live the longer, the 

 smaller the amount of water, provided the quantity does not 

 fall below a certain minimum." In Table V. I have collected 

 Bullet's data showing this point. The table shows that the 

 relation holds for both redistilled water and water distilled in copper 

 alone. The length of life in the water from the copper still is 

 proportionately shorter throughout. 



