5o8 POPULAR SCIENCE MONTHLY. 



struggle for existence. The risks to which the eggs are exposed are 

 indeed enormous. Many fail of fertilization; many are devoured or 

 otherwise destroyed. Nor do the dangers to which the salmon are 

 subject end with their hatching. Even if the growing fish escape the 

 voracity of the trout in their natal streams, a host of enemies await 

 them in the ocean. If the number of salmon from year to year remains 

 fairly constant, it is evident that the chances for any one egg surviving 

 to become a mature fish, to replace one of its parents and in turn have 

 offspring, would be represented by two, while the chances of destruction 

 would equal nearly the total number of eggs produced by the female, 

 which amount to many thousand. Yet compared to the dangers which 

 a deep-sea fish like the cod must escape, the hatching and early life 

 of the salmon in the lakes and streams probably offer great advantages. 

 Were the salmon to remain in fresh water, however, where the food 

 supply is limited, their numbers would be at least as limited as are 

 the trout. The same explanation probably holds good for their fasting 

 in fresh water. Were they to feed during the spawning season they 

 would leave nothing for the newly hatched fish, — and indeed the spawn 

 of the preceding year and their own eggs would form, as in the case 

 of other fish, a large part of their diet. 



In the salmon nature offers to science, on a scale far exceeding the 

 resources of any laboratory, an experiment in the metabolism of hunger 

 — a demonstration that the energy liberated within the animal body 

 comes not directly from the combustion of the carbonaceous substances 

 of the food, as the energy of a steam engine from its fuel, but from 

 the breaking down of the tissues themselves. Furthermore the condi- 

 tions are reduced to their simplest terms. In the warm-blooded animals 

 the maintenance of a temperature many degrees above their surround- 

 ings, necessitates a continual drain on the potential energy stored in 

 their tissues. In the cold-blooded salmon, on the other hand, lying 

 quietly, for weeks or months together, between the stones on the bottom 

 of the Rhine, the processes of oxidation sink to a minimum, involving 

 little else than the movements of the gills and the beating of the heart. 

 Thus the energy latent in the fats, carbohydrates and albuminous 

 substances, which the fish brings from the sea, is utilized almost 

 wholly in the contractions of the muscles ; and within the limits of the 

 dynamic efficiency of these tissues this force is expended in the 

 mechanical work of swimming. For physiologists the especial impor- 

 tance of this experiment lies in its bearing on the recent revival, in 

 modified form, of the theory of Liebig, that the heat of the body is 

 maintained by a combustion of the fats, but that the albuminous sub- 

 stances or proteids are the source of muscular work. Unfortunately 

 the data upon this subject collected by Miescher are only partially 

 available. The conclusions, however, at which he arrived, are sup- 



