FOOD OF t'ARNIVORA. 



25 



excrements., has disappeared, in the process 

 of respiration, as carbonic acid and water. 



Had the animal food been burned in a 

 furnace, the change produced in it would 

 only have differed in the form of combina- 

 tion assumed by the nitrogen from that 

 which it underwent in the body of the ani- 

 mal. The nitrogen would have appeared, 

 with part of the carbon and hydrogen, as 

 carbonate of ammonia, while the rest of the 

 carbon and hydrogen would have formed 

 carbonic acid and water. The incombusti- 

 ble parts would have taken the form of 

 ashes, and any part of the carbon uncon- 

 sumed from a deficiency of oxygen would 

 have appeared as soot, or lamp-black. Now 

 the solid exciements are nothing else than 

 the incombustible, or imperfectly burned, 

 parts of the food. 



In the preceding pages it has been as- 

 sumed that the elements of the food are con- 

 verted by the oxygen absorbed in the lungs 

 into oxidized products; the carbon into car- 

 bonic acid, the hydrogen into water, and the 

 nitrogen into a compound containing the 

 same elements as carbonate of ammonia. 



This is only true in appearance; the body, 

 no doubt, after a certain time, acquires its 

 original weight. The amount of carbon, 

 and of the other elements, is not found to be 

 increased exactly as much carbon, hydro- 

 gen, and nitrogen has been given out as was 

 supplied in the food ; but nothing is more 

 certain than that the carbon, hydrogen, and 

 nitrogen given out, although equal in 

 amount to what is supplied in that form, do 

 not directly proceed from the food. 



It would be utterly irrationable to suppose 

 that the necessity of taking food, or the 

 satisfying the appetite, had no other object 

 than the production of urea, uric acid, car- 

 bonic acid, and other excrementitious mat- 

 ters of substances which the system expels, 

 and consequently applies to no useful pur- 

 pose in the economy. 



In the adult animal, the food serves to re- 

 store the waste of matter; certain parts of 

 its organs have lost the state of vitality, 

 have been expelled from the substance of 

 the organs, and have been metamorphosed 

 into new combinations, which are amor- 

 phous and unorganized. 



The food of the carnivora is at once con- 

 verted into blood ; out of the newly formed 

 blood those parts of organs which have un- 

 dergone metamorphoses are reproduced. 

 The carbon and nitrogen of the food thus 

 become constituent parts of organs. 



Exactly as much carbon and nitrogen is 

 supplied to the organs by the blood, that is, 

 ultimately, by the food, as they have lost by 

 the transformations attending the exercise 

 ot their functions. 



What then, it may be asked, becomes of 

 the new compounds produced by the trans- 

 formations of the organs, of the muscles, of 

 the membranes and cellular tissue of the 

 nerves and brain? 



These new compounds cannot, owing to 



their solubility, remain in the situation 

 where they are fovmed, for a well known 

 force, namely the circulation of the blood, 

 opposes itself to this. 



By the expansion of the heart, an organ 

 in which two systems of tubes meet, which 

 are ramified in a most minute network of 

 vessels through all parts of the body, there 

 is produced a vacuum, the immediate effect 

 of which is, that all fluids which can pene- 

 trate into these vessels are urged with great 

 force towards one side of the heart by the 

 external pressure of the atmosphere. This 

 motion is powerfully assisted by the con- 

 traction of the heart, alternating with its ex- 

 pansion, and caused by a force independent 

 of the atmospheric pressure. 



In a word, the heart is a forcing pump, 

 which sends arterial blood into all parts of 

 the body ; and also a suction pump, by 

 means of which all fluids of whatever kind, 

 as soon as they enter the absorbent vessels 

 which communicate with the veins, are 

 drawn towards the heart. This suction, 

 arising from the vacuum caused by the ex- 

 pansion of the heart, is a purely mechanical 

 act, which extends, as above stated, to fluids 

 of every kind, to saline solutions, poisons, 

 &c. It is obvious, therefore, that by the 

 forcible entrance of arterial blood into the 

 capillary vessels, the fluids contained in 

 these, in other words, the soluble compounds 

 formed by the transformations of organized 

 parts, must be comj. ?lled to move towards 

 the heart. 



These compounds cannot be employed 

 for the reproduction of those tissues from 

 which they are derived. They pass through 

 the absorbent and lymphatic vessels into the 

 veins, where their accumulation would 

 speedily put a stop to the nutritive process, 

 were it not that this accumulation is pre- 

 vented by two contrivances adapted ex- 

 pressly to this purpose, and which may be 

 compared to filtering machines. 



The venous blood, before reaching the 

 heart, is made to pass through the liver; the 

 arterial blood, on the other hand, passes 

 through the kidneys ; and these organs sepa 

 rate from both all substances incapable ot 

 contributing to nutrition. 



Those new compounds which contain the 

 nitrogen of the transformed organs are col- 

 lected in the urinary bladder, and being ut- 

 terly incapable of any further application in 

 the system, are expelled from the body. 



Those, again, which contain the carbon 

 of the transformed tissues, are collected in 

 the gall bladder in the form of a compound 

 of soda, the bile, which is miscible with 

 water in every proportion, and which, pass- 

 ing into the duodenum, mixes with the 

 chyme. All those parts of the bile which,, 

 during the digestive process, do not lose 

 their solubility, return during that process 

 into the circulation in a state of extreme di- 

 vision. The soda of the bile, and those 

 highly carbonized portions which are not 

 precipitated by a weak acid (together making 



