[109] POND CULTURE. 575 



I am unable to decide which of these two Jialuralists is ii<'ht but I 

 deeui it proper to give both sets of figures. 



From the above it appears that fisli, compared witii warm-blooded 

 animals, need a small quantity of carbon, and conscMpicntly I'ewer hy- 

 drates of carbon in their food; and the approximate proportion of nulri- 

 tive substances, as given by us above becomes still more probable even 

 if it is not contirmed in all its details. It also appears that, with an ecjual 

 (juantity of food, lisli will grow more rapidly than land animals, because 

 in the same quantity of food they receive a much greater portion of al- 

 buminous matter which is changed to flesh and blood. This increavse 

 of weight in lish, which is sometimes marvelous, as the example of 

 Mr. Poppe's carp in California shows, proves that with an increased 

 (juantity of albumen, introduced into the body, there will be a corre- 

 sponding increase of Hesh and fat.* The groMth of the carj) is alsopro- 

 moted by the extraordinary digestive i^ower of w^hich these lish are pos- 

 sessed, and which among the rest is shown by the fact that they appro- 

 I>iiate from the excrements of animals nutritive substances which these 

 animals were not able to digest. 



We will now compare Avith the mostfavorable proportion of nutritive 

 substances, as calculated above, tlie proportion of these substances as 

 existing in the food which nature i)rovides for them in the ponds. 

 Besides vegetable matter and various nutritive substances dissolved in 

 the water, this foud comprises Morms, maggots, snails, beetles, and other 

 insects. lieetlesand insects generally, when dried, contain on an average 

 05 i)er cent of nitrogenous substances. As regards the nutritive matter 

 contained in worms, maggots, and snails, no observations ha\ e been 

 made. ])eliust is of opinion that the (inantjty of j)ioieine contained 

 in them is like that of the silk-worm, viz., 15 ])er cent; I think, how 

 ever, that this ])ercentage is too low as far as snails and maggots are 

 concerned, which latter are generated in flesh and blood; for they are 

 formed from strongly albumintuis substances, and therefore probably 

 contain a good deal of uitrogen. It is well-known that snails form a 

 very nutritious article of food, and probably contain much proteine. 

 ]Iowever this may be — for we cannot entertain mere suppositions — we 

 will take, as a tolerably safe basis, beetles and other insects and their 

 larvie (the former are formed from the material of the latter, and their 

 quantity of nitrogen will probably not vary much), which compose the 

 larger portion of the natural food of the carj). 

 The circumstance that the percentage of i)roteine (95) given above 

 I applies to dried beetles and insects, while carp always eat them alive, 

 I will not make any difl'erence in our present calculation, as tiie pro[)or- 

 I tion of nutritive substances remains the same, no matter whether the 

 • food is <lried or fresh. 

 ' According to Prof. E. Wolfl", the i^roportion of uutriti\'e substances 



* Wolff, Futteriinyslehre, p. 423, 

 t Dclius, Tcichwirihuchafi, 



