6 NUTRITION. 



two great vital organs are situated in the breast, and separated from the digestive and other 

 systems by a partition, which is scientifically known by the name of "diaphragm," and in 

 popular language by the term "midriff." This structure does not exist in the Birds ; and its 

 presence, together with that of the freely-suspended lungs, is an unfailing characteristic of the 

 Mammalian animal. 



Thus the entire structure bears the closest resemblance to a tree, growing with its root 

 upwards and its leaves downward, the trachea being the trunk, the branchial tubes the limbs, 

 the smaller tubes are the branches, and the air-cells the leaves. A similar idea runs through 

 the nerve system and that of the blood ; all three being interwoven with each other in a manner 

 most marvellous and beautiful. 



The ORGANS OF NUTRITION occupy the greater part of the space between the diaphragm 

 and the lower limbs, and are composed of the following parts. The mouth receives and, in 

 most cases, grinds the food until it is sufficiently soft to be passed onwards into the general 

 receptacle, called the stomach. Here begins the process of digestion, which is chiefly carried 

 on by means of a liquid called the gastric juice, which is secreted by glands within the stomach, 

 and dissolves the food until it is of a uniform soft consistency. In this state the food is called 

 "chyme," and passes from the stomach into a tube called the "duodenum." Here the chyme 

 begins to separate into two portions ; one, an indigestible and useless mass, and the other, 

 a creamy kind of liquid, called "chyle." The former of these substances is' propelled 

 through the long and variously-formed tube, called the intestinal canal, and rejected at its 

 outlet ; while the chyle is taken up by numerous vessels that accompany the intestines, 

 and is finally thrown into one of the large veins close by the heart, and there mixes with the 

 blood. 



There is another curious system called the "lymphatic," on account of the limpid appear- 

 ance of the liquid which is conveyed through the lymphatic vessels. These are analogous to 

 the lacteals, but instead of belonging to the intestines, they are spread over the whole frame, 

 being thickly arranged just under the skin. They are curiously shaped, being studded with 

 small knotty masses, and fitted with valves which keep the contained liquid in its proper 

 course. Both the lacteal and lymphatic vessels pour their contents into one large trunk, called 

 from its position the thoracic duct. This vessel is about twenty inches in length, and when 

 distended, is in its widest part as large as a common lead pencil. 



All these wonderful forms and organs would, however, be but senseless masses of matter, 

 differing from each other by the arrangement of their component paxts, but otherwise dead 

 and useless. It needs that the being which is enshrined in this bodily form (whether it be 

 man or beast) should be able to move the frame at will, and to receive sensations from the 

 outer world. 



More than this. As all vertebrated animals are forced at short intervals to yield their 

 wearied bodies to repose, and to sink their exhausted minds in the temporary oblivion of sleep, 

 there must of necessity be a provision for carrying on the vital functions without the active 

 co-operation of the mind. Were it otherwise, the first slumber of every being would become 

 its death sleep, and all the higher classes of animals would be extirpated in a few days. The 

 mind would be always on the stretch to keep the heart to its constant and necessary work ; 

 to watch the play of the lungs in regenerating the blood ; to aid the stomach in digesting the 

 food, and the intestinal canal in sifting its contents ; together with many other duties of a 

 character quite as important. 



Supposing such a state of things to be possible, and to be put in practice for one single 

 hour, how terrible would be the result to humanity ! We should at once degenerate into a 

 mass of separate, selfish individuals, each thinking only of himself, and forced to give the 

 whole of his intellectual powers to the one object of keeping the animal frame in motion. 

 Society would vanish, arts cease from the face of the earth, and the whole occupation of man 

 would be confined to living an isolated and almost vegetable life. 



This being the case with man, the results to the lower portions of the animal kingdom 

 would be still more terrible. For their intellect is infinitely below that of the dullest of the 

 human race, and they would not even possess the knowledge that any active exertion would 



