172 Investigations on the Life- History 



found either in the stomach or in the contents of the intestine. That 

 this is not due to rapid digestion has been proved. That it is not due 

 to the fish disgorging the contents of the stomach when caught is shown 

 by the absence of any trace of the indisgestible portions of worms, 

 insects, or fish in the intestine. 



To the unscientific mind it is perhaps difficult to realise the possibility 

 of a fast of several months in so active an animal as the salmon. But 

 it must be remembered that it is simply a question of supply of energy. 



The food yields energy for work, but if it is taken in excess, it is 

 stored so as to be available at a future period. It has been shown that 

 in the salmon such storage goes on to an enormous extent, and that, 

 even at the end of the fast, there is still plenty of material available to 

 meet any unexpected call for energy. Nor is the salmon exceptional in 

 this respect. Many other cold-blooded animals have the same power 

 of living for very prolonged periods without taking food, while several 

 warm-blooded animals during the rutting season undergo prolonged 

 fasts. It is stated that the male fur seal, after coming to land, may 

 live for over a hundred days without food. During this period he is 

 constantly engaged in struggles with other males, and he finally leaves 

 the shore in a state of extreme emaciation. 



We have thus no hesitation in confirming the conclusions of Miescher- 

 Ruesch that the salmon, at least before spawning, does not feed during 

 its sojourn in fresh water. 



C. CHEMICAL CHANGES IN THE SALMON IN FRESH WATER. 



It is because of this prolonged fast and because of the important 

 changes going on in the fish during the fast that it affords so interest- 

 ing a physiological study in metabolism. An opportunity is 

 afforded of investigating the manner in which materials are stored in the 

 animal body, the extent to which they may be transferred from one 

 organ to another, the nature of some of the chemical changes they 

 undergo, and the extent to which the various stored materials are 

 utilised as a source of energy in the body. 



/. Solids and Water of Miisde, Genitalia, etc. 



It has been shown that during the sojourn of the fish in fresh water 

 there is a steady loss of solids from the muscles and a steady gain of 

 solids by the genitalia, and it has further been shown that the gain of 

 solids by the genitalia is small compared with the loss of solids from the 

 muscle, that in fact the greater part of the solids lost from the muscles 

 are used for some other purpose than the building up of the genitalia 

 (p. 83). 



As the season advances, the fish coming to the estuaries have 

 a larger percentage of water in the muscle about 6 or 7 per cent, 

 more than the fish leaving the sea earlier in the season. In 

 the upper reaches the flesh throughout the season contains a greater 

 percentage of water than the flesh of estuary fish. In May and June 

 the upper-water fish have about 5 per cent, more water than the 

 estuary fish, and in October and November about 1 3 per cent, more 

 water than the estuary fish of May and June. 



It is this increase in the percentage of water of the flesh which main- 

 tains the weight of the fish per fish of standard length, although the 

 solids as a whole have diminished. 



//. Fats of Muscle, Genitalia, etc. 



Nothing is more extraordinary than the enormous accumulation of 

 fats which takes place in the muscle of the salmon during its visit to the 



