Animals do not feed upon unorganised matter, as do vegetables, but merely appropriate to their own use those organic principles which are ready formed in the vegetable or animal, such as albumen, fibrine, starch, gum, sugar, &c., and assimilate them into their substance.
FIG. 91.—LUNGS, HEART, AND LARGE VESSELS.
1 and 2, Right and left Lungs; 3, Heart; 4, Aorta; 5, Trachea.
When food enters the mouth of an animal it there meets with a fluid (the saliva) which is capable of converting starchy matters into sugar, thus rendering this aliment (which is presented in a state of a nature quite insoluble at the heat of the stomach) not only soluble, but nutritious. This ensalivation takes place while the food is being masticated; when in the stomach (fig. 90) it meets with the "gastric juice," a fluid capable of dissolving both fibrine and albumen (the two other chief aliments), even when coagulated; thus all kinds of food when they have been a short time in the stomach are reduced to a liquid, and so far fitted to enter the system. The stomach is a membraneous bag, communicating at the upper orifice with the mouth, and at the lower with the intestines; its internal (mucous) coat is smooth, and contains many absorbents; its outer coat is muscular, and capable of contraction, so as to roll together its contents, thus bringing every portion into contact with the gastric juice; this mass of dissolved food has received the name of "chyme." By admixture with the bile (a fluid excreted by the liver) and other juices, it separates (like curds and whey) into a liquid and partially solid matter; the liquid part is like milk, and is called "chyle," and it is taken up by absorbent vessels, by "endosmose," a peculiar power which membranes have of allowing liquids to pass through them when there is a more dense liquid on the other side (as described in the experiment at [page 123], "Vegetable Kingdom,"), and, passing through the vessels called "lacteals," is mixed there with the impure blood as it is about to be returned to the heart, and from thence to the lungs, where impurities are got rid of in the form of carbonic acid. The lungs (fig. 91), in performing this office, expose the blood (contained in thousands of minute blood-vessels) to the air which enters the windpipe at every inspiration or breath, the windpipe divides into two, and these each into two more (the bronchial tubes), and so on until they are no larger than a hair; at the end of each tube is a little "air-cell," on the membraneous walls of which the vessels containing the blood are distributed as a network. The blood when it enters the lungs is of a dark purple or blackish colour, and is loaded with carbonic acid; this blood is received by the heart from the great veins, which pour it into the right auricle, this contracting, sends it into the right ventricle, which, in turn, sends it through the pulmonary arteries into the lungs; while there, it is exposed in the network of vessels which ramify on the walls of the air-cells; another process of endosmose takes place, and the carbonic acid passes through the walls of the vessels into the air-tubes, and escapes by the breath; at the same time that this carbonic acid is cast off, an equal bulk of oxygen is absorbed from the air, so that the air which enters the lungs, and that which passes out, are the same in bulk—plus watery vapour—although what enters is pure air, and what is expelled, is loaded with carbonic acid. The blood, having exchanged carbonic acid for oxygen, is now altered from a black to a bright scarlet colour, and is in a condition to be circulated through the system. On leaving the lungs by the "pulmonary veins," it enters the left auricle of the heart, and passes from thence to the left ventricle, which is very powerful, and forces it by compression upwards into the "aorta" (the first great artery), and thence through the other arteries, which divide, and become smaller and smaller until it arrives at every part of the body, forming a network of fine vessels which are called capillaries; so perfectly are these vessels distributed, that it is almost impossible to cut or prick any part of the body without wounding one of them, and thereby drawing blood. When these capillaries have supplied this pure blood to repair and renovate every part of the system, and received for the new material, that which is worn out or spoiled, they urge it onwards to where they unite into small veins, and, as these continue to unite, they form large trunks, and pour the blood, now black and impure, into the right auricle of the heart, together with the fresh material (chyle) derived from the food, again to be sent through the lungs and purified for fresh circulation. This description applies as well to the other Mammalia as it does to Man, for these classes do not differ from Man in their physical structure, except in form and size, and the alteration in the proportion of the various parts to adapt each to its peculiar purpose.
EUROPEAN AND NEGRO.
Man is, without doubt, the only animal possessed of reflective and reasoning faculties, and the possession of these has raised him immeasurably above all the rest. He has also physical capabilities suitable to a dominant being whose race is destined to people the earth in every part. Were his constitution formed like that of the Chimpanzee or the Ourang, he could only live in the very hottest of climates; but it is found that Man is healthy and happy through ranges of temperature, which would prove fatal to most other animals. In the frigid regions of the north, the Laplander enjoys many comforts which he fancies could never be obtained in any other latitude, and the Bushman of Africa, following the wild animals of that region, and needing no covering to shield him from the burning rays of the sun, deems his lot the happiest that can be. The human race are gradually increasing in number, and there is scarcely a spot capable of being inhabited at all, but they are found there; and, wherever Man comes, the wild animals of the region retire or become entirely extinct, excepting those which serve him as food, such as the Ruminants.
The difference between the highest of the lower animals and Man, is so distinct, that no more need be said about it; but among men themselves, there is a great difference; between the European, and the Negro or the Hottentot, there is a vast distinction, but the most simple would at once say they are both men, and possessed of the essential qualities of men; and there can be no doubt that all men of every kind form one species. This is a point pretty well settled among all who have written on the subject; and indeed, great as the difference is among men, it is not half so great as that which exists between the Bull-dog and Italian Greyhound, and yet they are both dogs; or between the Race-horse and the Dray-horse, and yet who is there can doubt of these both being of the same species.
Blumenbach made out five varieties—namely, 1, Caucasian; 2, Mongolian; 3, American; 4, Malay; 5, Ethiopian or Negro. Pickering[2] describes eleven varieties, and arranges them as follows:—