[107] POND CULTURE. 573 



food used iu these experiments was hay of uiediuin quality and tlie 

 l)ropoition of nutritive substances was probably the foUowin-'-: 



Nh : Nfr = 1:7. 



As was stated above, the tench exhaled per 100 pounds weight in 

 twenty-fourhours, V2 grams carbon, while the sheep exhaled 222.5 grams 

 therefore 18.5 times as much. We now know the quantity of carbon 

 consumed and exhaled by sheep per 100 pounds live weight, and when a 

 certain kind of food is employed; we also know the quantity of carbon 

 exhaled by an equal weight of tench, and we can therefrom easily cal- 

 culate the quantity of carbon consumed by tench. We are, therefore, 

 enabled, since we have three known quantities, to find the fourth one by 

 the following i)roportion : 



222.5 grams : 12 grams = 7 Nfr. : x Nfr. 



12 y 7 



We get the same result if we say that the proportion between the 'ab- 

 sorption of carbon with the food of sheep and the absor[)tiou of carbon 

 by the tench — Avhich is found by the following proportion : 222.5 : 12 = 

 481.3 : X, i. c, x = 25.9 — is as follows : 



481.3 : 25.9 = 7 : x, whence x = 0,38. 



The |)roportion of nutritive substances in food, therefore is, for sheep, 

 Xh : Nfr = 1:7; carp = 1 : 0.38. 



As the :ibsori)tion of nutritive substances in the ditterent kinds of hay 

 varies from 1 : 5.1 to 1 : 10.0, and as we do not know what kind of hay 

 was used in the experiments made at Wende, the proportion of nutri- 

 tive substances in the food of the carp will i>robably vary between 0.27 

 and 0.57. It can hardly be supposed, however, that the hay used in 

 the experiments referred to was anything but hay of a medium quality, 

 as first-class hay is but rarely met with in that locality. The difference 

 will, therefore, be only between 1 : 7 and 1 : S, and for the carp between 

 0.38 and 0.13. 



Although this whole calculation is somewhat bohl, and absolute cor- 

 rectness cannot be claimed for its results, it is probable that these are 

 at any rate approximately correct. This i)roportion of nutritive sub- 

 stances is very close; but we will ha%e to acloiowledge its ajjproximate 

 correctness, if we take into consideration the following facts: 



1. For generating and maintaining the normal degree of heat in tlie 

 body of warm-blooded animals (witli man, 37° Centigrade [98p F.] ) 

 a certain quantity of carbon, and therefore of hydrates of eaibon, is 

 needed, which, in connection with the oxygen inhaled, causes the de- 

 struction (by a burning i)rocess) of fat in' the animal body, by which 

 heat is generated. Fish have no heat of their own, therefore need no 



