ORIGIN OF FAT IN ANIMALS. 



31 



and so small a portion of alkaline phos- 

 phates as to have been overlooked by most 

 observers. 



The deficiency or absence of alkaline 

 phosphates in the urine of the graminivora, 

 obviously indicates the slowness with which 

 the tissues in this class of animals are meta- 

 morphosed ; for if we assume that a horse 

 consumes a quantity of vegetable fibrine 

 and albumen corresponding to the amount of 

 nitrogen in his daily food (about 4$ oz.,) and 

 that the quantity of tissue metamorphosed 

 is equal to that newly formed, then the 

 quantity of phosphoric acid which on these 

 suppositions would exist in the urine is not 

 so small as not to be easily detected by analy- 

 sis in the daily secretion of urine (3 Ibs. 

 according to Boussingault ;) for it would 

 amount to 0.8 per cent. But, as above 

 stated, most observers have been unable to 

 detect phosphoric acid in the urine of the 

 horse. 



Hence it is obvious that the phosphoric 

 acid which in consequence of the metamor- 

 phosis of tissues is produced in the form of 

 soluble alkaline phosphates, must re-enter 

 the circulation in this class of animals. It 

 is there employed in forming brain and ner- 

 vous matter, to which it is essential, and 

 also, no doubt, in contributing to the supply 

 of the earthy part of the bones. It is pro- 

 bable, however, that the greater part of the 

 earth of bones is obtained by the direct as- 

 similation of phosphate of lime, while the 

 soluble phosphates are better adapted for the 

 production of nervous matter. 



In the graminivora, therefore, whose food 

 contains so small a proportion of phos- 

 phorus or of phosphates, the organism col- 

 lects all the soluble phosphates produced by 

 the metamorphosis of tissues, and employs 

 them for the developement of the bones and 

 of the phosphorised constituents of the 

 brain ; the organs of excretion do not sepa- 

 rate these salts from the blood. The phos- 

 phoric acid, which, by the change of matter, 

 is separated in the uncombined state, is not 

 expelled from the hody as phosphate of soda ; 

 but we find it in the solid excrements in the 

 form of insoluble earthy phosphates. 



XVI. If we now compare the capacity 

 for increase of mass, the assimilative power 

 in the graminivora and carnivora, the com- 

 monest observations indicate a very marked 

 difference. 



A spider, which sucks with extreme vo- 

 racity the blood of the first fly, is not dis- 

 turbed or excited by a second or third. A 

 cat will eat the first, and perhaps the second 

 motive presented to her, but even if she kills 

 a third, she does not devour it. Exactly 

 similar observations have been made in re- 

 gard to lions and tigers, which only devour 

 their prey when urg^d by hunger. Carni- 

 vorous animals, indeed, require less food for 

 their mere support, because their skin is 

 destitute of perspiratory pores, and because 

 they consequently lose, for equal bulks, 

 much less heat than 2r,iiuinivorous ani- 



mals, which are compelled to restore the 

 lost heat by means of food adapted for 

 respiration. 



How different is the energy and intensity 

 of vegetative life in the graminivora. A 

 cow, or a sheep, in the meadow, eats, almost 

 without interruption, as long as the sun is 

 above the horizon. Their system possesses 

 the power of converting into organized tis- 

 sues all the food they devour beyond the 

 quantity required for merely supplying the 

 waste of their bodies. 



All the excess of blood produced is con- 

 verted into cellular and muscular tissue; the 

 graminivorous animal becomes fleshy and 

 plump, while the flesh of the carnivorous 

 animal is always tough and sinewy. 



If we consider the case of a stag, a roe- 

 deer, or a hare, animals which consume the 

 same food as cattle and sheep, it is evident 

 that, when well supplied with food, their 

 growth in size, their fattening, must depend 

 on the quantity of vegetable albumen, fibrine, 

 or caseine, which they consume. With 

 free and unimpeded motion and exercise, 

 enough of oxygen is absorbed to consume 

 the carbon of the gum, sugar, starch, and of 

 all similar soluble constituents of their 

 food. 



But all this is very differently arranged in 

 our domestic animals, when with an abun- 

 dant supply of food, we check the processes 

 of cooling and exhalation, as we do when 

 we feed them in stables, where free motion 

 is impossible. 



The stall-fed animal eats, and reposes 

 merely for digestion. It devours in the 

 shape of nitrogenized compounds far more 

 food than is required for reproduction, or the 

 supply of waste alone ; and at the same 

 time it eats far more of substances devoid 

 of nitrogen than is necessary merely to sup- 

 port respiration and to keep up animal heat. 

 Want of exercise and diminished cooling 

 are-equivalent to a deficient supply of oxy- 

 gen ; for when these circumstances occur, 

 the animal absorbs much less oxygen than 

 is required to convert into carbonic acid 

 the carbon of the substances destined for 

 respiration. Only a small part of the ex- 

 cess of carbon thus occasioned is ex- 

 pelled from the body in the horse and ox, 

 in the form of hippuric acid ; and all the re- 

 mainder is employed in the production of a 

 substance which, in the normal state, only 

 occurs in small quantity as a constituent 

 of the nerves and brain. This substance 

 is fat. 



In the normal condition, as to exercise 

 and labour, the urine of the horse and ox 

 contains benzoic acid (with 14 equivalents 

 of carbon ;) but as soon as the animal is 

 kept quiet in the stable, the urine con- 

 tains hippuric acid, (with 18 equivalents 

 of carbon.) 



The flesh of wild animals is devoid of 



fat; while thai of stall-fed animals is 



covered with that substance. When the 



I fattened animal is allowed to move rnor 



