Page:Popular Science Monthly Volume 60.djvu/517

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ported by the thorough investigation of Dr. Noël Paton and his coworkers of the Scottish Fishery Board on the salmon of their rivers. They have determined the amount of the various fuel materials which disappear from the bodies of the salmon during their journey up stream. For this purpose they have analyzed all the tissues and organs of numerous salmon taken from the estuaries in the spring and early summer, just as the fish were starting up the rivers. They also found the amount of fat and albuminous material remaining in the tissues of the fish taken from the head waters of the rivers, a month or so later. By calculating from the numerical results of these analyses the equivalent figures for a fish of 'standard length'—arbitrarily taken at one meter—a fairly accurate basis of comparison was obtained. On this basis the difference in the composition of the tissues of the fish of the estuaries, and those of the head waters, reveals the number of grams of fat and albuminous material which the journey up stream costs the fish. The results show that, varying with the length of their journey—which in no case approaches the distance up the Rhine—the swiftness of the current overcome, and the other exertions necessary, the salmon in passing from the estuaries to the head waters, expend three hundred to six hundred grams of fat, and only sixty to a hundred and twenty grams of albuminous material. In the animal body the combustion of the fats and sugars is complete. They leave the system in the form of carbonic acid and water, after liberating within the tissues precisely that amount of energy which they would yield as heat, if burned in a perfect lamp or the most accurately constructed calorimeter. For the albuminous substances the combustion is less complete; but the amount of energy which comes from each gram decomposed within the body is determinable with no less accuracy than for the fats. To find the energy which the salmon expend in the ascent of the Scottish rivers, it is only necessary, therefore, to multiply the amount of fuel material expended by the number of calories which one gram of fat or albuminous material yields in a calorimeter. Thus it is found that the same six hundred grams of fat and one hundred and twenty grams of proteid, which the journey up the longer rivers costs the salmon, would heat sixty-five liters of water from the freezing point to boiling, or, to express the same amount in terms of mechanical work—would, if theoretical conditions in this regard were attainable, lift fourteen kilos (the weight of the 'standard fish' of the Scottish investigations) to the height of a hundred and eighty kilometers. But it must be borne in mind that the dynamic efficiency of few engines devised by man exceeds fifteen per cent.; and the investigations of physiologists have shown that the contracting muscles develop an efficiency only five to ten per cent, greater. From such data as these, together with the rate of flow of rivers, their length, and the time