Section I.
Bodily Constitution of Man

Chapter 1.
Material Frame of Man.

When we direct attention to the varied properties of matter we find that those of which mechanical philosophy takes cognizance, extension, form, mobility, and weight, pervade the whole creation here below. Every object has some definite size and form, every object is influenced by the attraction of gravitation, and can be put in motion if a force sufficient be applied. Every substance, we also remark, whether it exist in the solid, fluid, or aeriform state, is subject to certain fixed and determinate laws. All these properties, on which the sciences of mechanics, hydrostatics, and pneumatics depend, are found in the material frame of man. We find, moreover, every bone and muscle, every vein and vessel, so admirably adapted to the purposes for which it is designed, that the human frame, viewed simply as a machine, constrains us to say with the Psalmist, "We are fearfully and wonderfully made."

Besides these properties, which pervade the whole visible creation, there are others, such as cohesion, crystallization, and chemical affinity, which, in one form or another, are very generally diffused. These, also, we find in man; and the adaptation which we observe between them and the various organs of our body, afford manifold evidence of the wisdom, power, and goodness of the Creator. On this subject, however, we do not enter. Even if it lay directly in the path of our inquiry, it has already been amply discussed. In Paley's Natural Theology, in the Bridgewater Treatises, and in a multitude of similar publications, the wonders of the human frame are fully described, and the evidences which they afford of the Creator's benevolent design are clearly displayed.

We also remark, that the general properties of matter, whether mechanical or chemical, are variously modified by heat, light, electricity, and the other imponderable agents. These all exert their influence on man, and that influence is eminently conducive to his well-being and enjoyment.

In order to shew how admirably our bodily frame is adapted to the effects produced by these mysterious agents, we may refer, as a passing illustration, to the means by which that uniform temperature is secured, without which the vital functions cannot be sustained; and in order to shew more clearly the perfec­tion of contrivance which they exhibit, we shall compare them with those appliances which man adopts when he wishes to secure a similar end.

The knowledge which man has acquired of the properties of heat, and the skill he has manifested in rendering this mighty agent subservient to his comfort, are amongst the most striking proofs we have of the superiority of the human intellect over that of the lower animals. When we look to the irrational creatures, we find them so little acquainted with the properties of heat, and so little practised in the appliances by which it may be regulated, that their utmost skill only enables them to seek a sheltered nook, to dig a burrow, or build a nest, to protect them from the cold. But if we examine the abodes of man, and mark the contrivances which he employs to secure a temperature congenial to his feelings, we see at a glance that he belongs to a superior rank and order in creation. He has walls and roofs, which exclude alike the winter's cold and the summer's sun; he has windows and doors, which can be opened and shut at pleasure, to warm or to cool his dwelling. In order to raise the temperature of the house above that of the surrounding atmosphere, he kindles fires in the various apartments, and so contrives the fireplace that, while the warmth is retained, the smoke and noxious compounds are carried away. On the other hand, when he wishes his dwelling to be a shelter from the heat, a projecting roof excludes the burning rays, and gives a grateful shade, while open doors and windows supply a current of air. When he desires not only to exclude the sunshine, and admit a current of air, but to reduce, as is sometimes desirable, in India, for in stance, the temperature of his dwelling below that of the surrounding atmosphere, the passages by which air is admitted to the house are hung with wetted matting, and the rapid evaporation of the moisture absorbs the heat of the entering current, so that the inmates can enjoy a cooling breeze in the midst of a torrid plain.

In these adaptations and contrivances, we have evident proofs of the knowledge and art of man; and it is very interesting to observe that we have precisely similar evidences of the wisdom of the great Creator, in the varied arrangements by which the internal temperature, necessary for the functions of the animal economy, is preserved and regulated in the bodies of man and other animals.

The contrivances to which we have referred have three objects in view: to prevent too free a communication with the open air; to heat our dwellings when cold; and to cool them when warm. To accomplish the first of these objects, we employ walls and roofs, doors and windows, curtains, carpets, and similar articles of furniture. The same purpose, however, is far more wonderfully accomplished by the clothing which Nature has provided for the various classes of animals. Those quadrupeds which live in the colder regions of the earth have an external covering of hair or wool, which varies in thickness and closeness of texture according to the habits of the creature on which it is bestowed, and to the degree of cold to which it is exposed. It is closer and thicker, for instance, in animals that seek their food by night than it is in those that seek their food by day; it is thicker in winter than it is in summer, and in the arctic regions than in the temperate zones. Birds, which are exposed to great vicissitudes of temperature in their passage through the air, have a still more wonderful provision made for their comfort. They require, if we may so express it, a coat at once of greater warmth and of a lighter fabric. Such a covering has been provided for them in the down and feathers with which they are clad. The feathers, moreover, we find thicker and closer in web-footed fowls that swim on the water, than in birds that live on the land; softer and warmer in the owl that preys by night, than in the falcon that flies by day. In the class of cetaceae or whales, which, while they live wholly in the water, and have the form of fishes properly so called, possess the warm blood and internal organization of animals that live on land, the mass of blubber that lies between their flesh and the outer hide, accomplishes the same purpose that is served by the feathers of the bird and the fur of the quadruped. All these coverings, however different in appearance and in nature, are designed to protect the creatures which they cover from the influence of the cold, and this purpose they most effectually fulfil. We do not find any such clothing provided for man. He is left to the exercise of his own industry and skill; but the coverings given to animals serve at once to shew him the pattern he should follow, and to provide the material he requires.

We observe farther, that, to increase the comfort of his dwelling, man not only excludes the open air, but employs the varied apparatus of fireplaces, stoves, and flues. By these means he brings together a supply of fuel and air, he effects a chemical combination between them in the fire, he conveys away the noxious compounds that are formed, while he retains for his own use and comfort the heat which that combination has evolved. Some may perhaps be startled when they are told that a precisely similar process is going on continually within us. Yet so it is. The lungs are the fireplace, if we may so speak, of the animal system. The blood that is brought into them by the veins, from every extremity of the body, comes loaded with carbonaceous matter, which, after having served its purpose in supporting and refreshing the various members, is brought into the lungs, and is there united to the air that is inhaled through the nostrils—a combination precisely similar to that which is formed in combustion then takes place, the next expiration carries off the contaminated air, while the blood, purified and swarmed, passes through the heart and arteries, and diffuses a genial warmth throughout the frame. The lungs are thus the fireplace where the combustion takes place—the veins bring in the fuel, the arteries carry off the heat, while the windpipe is alternately the bellows that blow the fire and the chimney that carries the smoke away.

We also remarked that, in order to avoid the opposite extreme of too high a temperature, recourse is sometimes had to the use of wetted matting, that, through the process of evaporation, the heat may be reduced. A similar operation goes on in the animal economy. While the union of carbonaceous matter with the air in the lungs produces heat, the evaporation of the watery particles of the blood, which goes on simultaneously with that combination, modifies the heat produced, and prevents injurious excess. This cooling process is also aided by the insensible perspiration, which carries off moisture from the pores of the skin.

There are thus going on continually within us a process for cooling and a process for heating; and so beautifully are they attempered to each other, that whatever the circumstances may be in which we are placed in regard to the external heat or cold, so long as life remains unimpaired, the warmth of the vital parts scarcely experiences any alteration. The human system is so admirably arranged, that the colder it is the greater is the supply of carbonaceous matter thrown into the blood and brought into the lungs, and the warmer it becomes the more are the watery particles increased. All must have observed that our appetite for food is quickened by exposure to the wintry air, and some perhaps may have wondered at this increased desire for sustenance. Arctic voyagers tell us that when sailors go to the polar regions, they must be served with a double allowance of provisions. This increased desire for sustenance is simply the demand which Nature makes for a larger supply of the carbonaceous matter contained in our food, to serve as fuel for the inward fire, in order that an increase of the internal heat may enable us to resist the effects of the greater external cold. On the other hand, when we pant in the heat of a midsummer's noon, our appetite for food is diminished, while our thirst is greatly in. creased. In this case the system endeavours, by a large exhalation of moisture, to counteract the effect of the external heat. So wonderfully are these two processes adjusted to each other, that if a due supply of food in the one case, and of water in the other, be given, we may breathe an atmosphere so far below zero, that quicksilver becomes solid as lead, and the warmth of the blood will exhibit no perceptible diminution; and we may be shut up in an oven, as various experiments have proved, till flesh be roasted, and water be made to boil, and the temperature of the body will scarcely indicate any increase.

This adaptation of the human frame to the varied properties of heat may serve as an illustration of the wonderful manner in which the body of man is constructed, and his different members adapted to the purposes for which they are designed. Into this subject, however, it would be foreign to the subject of our inquiry any further to enter.