10 iO REPORT OF COMMISSIONER OF FISII AND FISHERIES. [2] 



per 100 pounds of living- weight (luring < wenty-four Lours : by the tench, 

 12 grams; the frog, 13.5 grams; n)an, 14() grams; a pigeon, 1370 grams; 

 which would give the following proportion : 1 : 3.5=12 : 111. 



These investigations show an astonishingly small quantity of carL)<)n 

 exhaled by tisli, as represented by the tench. As the quantity of car- 

 bon exhaled varies accoidiug to the quantity received with the food, it 

 results from these investigations — which agree with those made by 

 Bousinganlt and in Wende — that the quantity of hydrates of carbon 

 mentioned in the rule for feeding is hardly too low. 



This small demand for hydrates of carbon is explained as follows: 



1. In warm blooded animals a considerable portion of the carbon re- 

 ceived with the food is used for producing warmth, as in conjunction 

 with the oxygen inhaled it occasions the burning of fat in the animal's 

 body. 



This demand does not exist in fish, as the body possesses no heat of its 

 own ; the demand for hydrates of carbon is hmited to the quantity 

 required for burning those substances which in the process of life be- 

 come waste matter ; and the quantity of carbon required for this pur- 

 pose is of course very small. 



2. Compared with land animals, fish make a small outlay of strength 

 in locomotion. Even for standing quietly the laud animal makes use of 

 the n)uscles, and when walking requires them to support the weight of 

 the body, but fish may float in the water or rest on the bottom without 

 iiuy special effort, because the water, its weight being equal to their 

 own, holds them up. 



This will become self-evident when we think of the ease with which 

 a man can move a raft in still water, whilst on land he would hardly 

 be able to move a single log of this same raft. It is true that swim- 

 ming very soon tires a man, but this is not owing to the amount of 

 strength required for the exercise, but simply to the fact that those mus- 

 cles which come into play are not accustomed to this kind of exercise. 



The circumstance that fish need much less exertion for their usual 

 motions than land animals is an explanation of their small demand for 

 hydrates of carbon and fat in their food. If, as is fully established, hard 

 work does not so much promote the destruction of albuminous matter 

 in the animal body as it intensifies the burning of hydrates of carbon 

 (which demands an increase in the quantity of oxygen inhaled by the 

 respiratory organs, which again creates greater heat, of which, how- 

 ever, a larger quantity is expelled from the body simultaneously with 

 a greater evaporation of moisture), the contrary must be the case under 

 the conditions of the life of fish. 



3. The elementary composition of the carp also favors a small de- 

 mand for hydrates of carbon, for, according to Dr. Konig, of Miinster, 

 this composition does not contain any substances free from nitrogen, 

 and, according to Prof. E. Wolti", the carp only possesses 4 per cent, of 

 extractives {Extract ivsioffc). The difference betw' een the investigations 



