24 



ANIMAL CHEMISTRY. 



Now, the analysis of caseine has led to the i stricter, a goat, a rabbit, or a bird, we find 



tnat the hair, hoofs, horns, feathers, or bones 

 of these animals, are expelled from the body 

 apparently unchanged. They have retained 

 their natural form and aspect, but have be- 

 come brittle, because of all their component 

 parts they have lost only that one which 

 was capable of solution, namely, the gela- 

 tine. Faeces, properly so called, do not 

 occur in serpents any more than in carnivo- 

 rous birds. 



We find, moreover, that when the serpent 

 has regained its original weight, every other 

 part of its prey, the flesh, the blood, the 

 brain, and nerves, in short, every thing has 

 disappeared. 



The only excrement, strictly speaking 

 is a substance expelled by the urinary pas r 



result, which, alter the details given in me 

 last section, can hardly excite surprise, that 

 this substance also is identical in composi- 

 tion with the chief constituents of blood, 

 fibrine and albumen. Nay, more, a com- 

 parison of its properties with those of veget- 

 able caseine has shown that these two sub- 

 stances are identical in all their properties; 

 insomuch that certain plants, such as peas, 

 beans, and lentils, are capable of producing 

 the same substance which is formed from 

 the blood of the mother, and employed in 

 yielding the blood of the young animal. (9) 



The young animal, therefore, receives, in 

 the form of caseine, which is distinguished 

 from fibrine and albumen by its great solu- 

 bility, and by not coagulating when heated, 

 the chief constituent of the mother's blood. 

 To convert caseine into blood no foreign 

 substance is required, and in the conversion 

 of the mother's blood into caseine, no ele- 

 ments of the constituents of the blood have 

 been separated. When chemically ex- 

 amined, caseine is found to contain a much 

 larger proportion of the earth of bones than 

 blood does, and that in a very soluble form, 

 capable of reaching every part of the body. 

 Thus, even in the earliest period of its life, 

 the development of the organs, in which vi- 

 tality resides, is, in the carnivorous animal, 

 dependant on the supply of a substance, 

 identical in organic composition with the 

 chief constituents of its blood. 



What, then, is the use of the butter and 

 the sugar of milk? How does it happen 

 that these substances are indispensable to 

 life? 



Butter and sugar of milk contain no fixed 

 bases, no soda or potash. Sugar of milk has 

 a composition closely allied to that of the 

 other kinds of sugar, of starch, and of gum; 

 all of them contain carbon and the elements 

 of water, the latter precisely in the propor- 

 tion to form water. 



There is added, therefore, by means of 

 these compounds, to the nitrogenized con- 

 stituents of food, a certain amount of carbon, 

 or, as in the case of butter, of carbon and 

 hydrogen ; that is, an excess of elements, 

 which cannot possibly be employed in the 

 production of blood, because the nitrogenized 

 substances contained in the food already 

 contain exactly the amount of carbon which 

 is required for the production of fibrine and 

 albumen. 



The following considerations will show 

 that hardly a doubt can be entertained, that 

 this excess of carbon alone, or of carbon and 

 hydrogen, is expended in the production of 

 animal heat, and serves to protect the or- 

 ganism from the action of the atmospheric 

 oxygen. 



XI. In order to obtain a clearer insight 

 into the nature of the nutritive process in 

 both the great classes of animals, let us first 

 consider the changes which the food of the 

 carnivora undergoes in their organism. 



If we give to an adult serpent, or boa con- 



When dry, it is pure white, like 

 chalk; it contains much nitrogen, and a 

 small quantity of carbonate and phosphate 

 of lime mixed with the mass. 



This excrement is urate of ammonia, a 

 chemical compound, in which the nitrogen 

 bears to the carbon the same proportion as 

 in bicarbonate of ammonia. For every equi- 

 valent of nitrogen it contains two equiva- 

 lents of carbon. 



But muscular fibre, blood membranes, 

 and skin, contain four times as much carbon 

 for the same amount of nitrogen, or eight 

 equivalents to one ; and if we add to this the 

 carbon of the fat and nervous substance, it 

 is obvious that the serpent has consumed 

 for every equivalent of nitrogen, much more 

 than eight equivalents of carbon. 



If now we assume that the urate of am- 

 monia contains all the nitrogen of the animal 

 consumed, then at least six equivalents of 

 carbon, which were in combination with this 

 nitrogen, must have been given out in a dif- 

 ferent form from the two equivalents which 

 are found in the urate of ammonia. 



Now we know, with perfect certainty, 

 that this carbon has been given out through 

 the skin and lungs, which could only take 

 place in the form of an oxidized product. 



The excrements of a buzzard which had 

 been fed with beef, when taken out of the 

 rectum, consisted, according to L. Gmelin 

 and Tiedemann, of urate of ammonia. In 

 like manner, the faeces in lions and tigers 

 are scanty and dry, consisting chietiy of 

 bone earth, with mere traces of compounds 

 containing carbon ; but their urine contains, 

 not urate of ammonia, but urea, a compound 

 in which carbon and nitrogen are to each 

 other in the same ratio as in neutral carbon- 

 ate of ammonia. 



Assuming that their food (flesh, &c.) 

 contains carbon and nitrogen in the ratio of 

 eight equivalents to one, we find these ele- 

 ments in their urine in the ratio of one equi- 

 valent to one ; a smaller proportion of car- 

 bon, therefore, than in serpents, in which 

 respiration is so much less active. 



The whole of the carbon and hydrogen 

 which the food of these animals contained, 

 beyond the amount which we find in their 



