278 MORRIS M. WELLS 



If we consider the different reactions of the salmon to current, 

 acidity, and density, at different stages in the hfe cycle, begin- 

 ning with the hatching of the egg we may proceed as follows. 

 It is a well established fact (Loeb '13) that in the fertilized egg 

 and newly hatched fry, the rate of oxidation is high, and it seems 

 to be clear (Wells '13) that from this time on, up to sexual maturity 

 the rate runs down. That is, the rate varies inversely with the 

 age of the fish. Salmon eggs hatched in fresh water must develop 

 into fry which are able to live in slightly acid water, of relatively 

 low density, and the fishes must also be positive to current or 

 they will be swept from the stream. This we find is true and 

 thus ability to live in fresh water is correlated at this time with 

 a high metabolic rate. As time goes by, however, the rate 

 of reaction becomes gradually lower until we find the fishes either 

 becoming actively negative, or at least indifferent to current, 

 and they are swept or swim into the ocean. They now live for 

 some time in the alkaline water of the ocean, and are able to 

 withstand its much higher densit3^ The equilibrium between 

 the environment and the organism is again disturbed after a 

 time, however, and we find the fishes once more selecting the fresh 

 water at another period of high metabolic rate, i.e., with the ma- 

 turing of the sex glands. From this it w^ould seem entirely 

 possible that fishes which are normally fresh water forms might 

 be temporarily transformed into salt water forms by regulating, 

 that is lowering, the rate of metabolism. 



With regard to the selection of the water of greater or lesser 

 density, the data presented in this paper offer an interesting 

 possibility. It has been shown that fresh water fishes whose 

 metabolic rate has been lowered by starvation, will select a 

 notably higher concentration of CaClo in the gradient than will 

 normal fishes. Also older, fishes select a higher concentration 

 than do younger ones. Thus a lowering of the metabolism causes 

 the fishes to choose a medium with higher specific gravity than 

 that normally chosen. It will be remembered furthermore that 

 a stay of a little less than a week in O.OIN C'aCl2 solution caused 

 a fish that was normally negative to this concentration in a 

 gradient, to become positive. Upon being returned to the tap 



