Sidor som bilder
PDF
ePub

Of God, as with a mantle, didst invest The rising world of waters dark and deep, Won from the void and formless infinite!" "Universal space, as far as we know of it," says Dr. Franklin, "seems to be filled with a subtile fluid, whose motion or vibration is called light; but I am not satisfied with the doctrine that supposes particles of matter, called light, are continually driven off from the sun's surface, with a swiftness so prodigious as philosophers suppose. Must not the smallest particle conceivable have, with such a motion, a force exceeding a 24-pounder discharged from a cannon? Must not the sun diminish exceedingly by such a waste of matter? and the planets, instead of drawing near to him, as some have feared, recede to greater distances through the lessened attraction. Yet these particles, with this amazing motion, will not remove the least and slightest dusk they meet with, and the sun, for aught we know, continues of his ancient dimensions, and his attendants move in their ancient orbits. May not all the phenomena of light be more conveniently solved by supposing universal space filled with a subtile and elastic fluid, which, when at rest, is not visible, but whose vibrations affect that fine sense in the eye, as those of air do the grosser organs of the ear? We do not, in the case of sound, imagine that any sonorous particles are thrown off, from a bell for instance, and fly in straight lines to the ear; why must we believe that luminous particles leave the sun and proceed to the eye? Some diamonds, if rubbed, shine in the dark, without losing any part of their matter. I can make an electrical spark as big as the flame of a candle, much brighter, and therefore visible farther; yet this is without fuel and I am persuaded that no part of the electric fluid flies off in such case to distant places, but that all goes directly, and is to be found in the place to which I destine it."

[ocr errors]

"By light," says the Abbé Pluché, we do not mean that sensation which we experience in ourselves, on the presence of any illuminated body, but that inconceivably subtile matter which makes an impression on the organ of sight, and paints on the optic nerve those objects from the surface of which it was reflected to us."

Taken in this sense, light is a body quite different from the sun, and might have existed before it, seeing that it now exists in its absence as well as when present. It is diffused from one end of the creation to the other, traverses the whole universe, forms a communication between the most remote spheres, penetrates into the inmost recesses of the earth, and only waits to be put in motion to make itself visible. Light is to the eye what the air is to the ear; air cannot be called the body of sound, though it equally exists all around us, when there is no sonorous body to put it in motion; so the light equally extends, at all times, from the most distant fixed stars to us, though it then only strikes our eyes when impelled by the sun, or some other mass of fire. The body of light, therefore, either exists independently of the luminous body, or we must suppose that every luminous body, whether it be the sun, a candle, or a spark, produces this light from itself, and projects it to a great distance; but to assert the latter is to assert a very great improbability; for if a spark which is seen in every part of a large room fifty cubic feet in dimensions, emits from its own substance a quantity of light sufficient to fill the whole room, then there must issue from that spark, which is but a point, a body the contents of which are fifty cubic feet. How incredible the supposition! On the contrary, how simple and natural is it to suppose that, as the air existed before the bell that put it in motion, so, in like manner, the light existed in the room before the spark was struck which excited its "It appears," says Dr. J. Taylor, in his vibrations and made it visible. Thus, the "Scheme of Scripture Divinity," "from sun and stars made themselves visible withelectrical experiments, that light is a dis-out suffering any diminution of substance; tinct substance from all others, as much as God having placed between those luminous air is from water, and that by being pro-globes and us the body of that light which perly excited, it may be made to appear in we see, and which is impressed on the organs midnight darkness; which shows that it did of vision by their actions and influence, but exist in that darkness previously to its being which does not proceed from them, nor owe excited, and that it was rendered visible by its existence to them. The account of Moses, being excited. Consequently it may, and I therefore, is agreeable to truth, as well as a doubt not doth, exist, expanded through the useful lesson of caution, when he informs us whole visible system of things at all times, that God, and not the sun, was the author by night as well as by day, and that the sun of light; and that it was created by His Alis in our system the great exciter, by which mighty fiat before there was a sun to dart the substance of light is impelled and be it on one part of the earth, and a moon to recomes visible." flect it on the other.

[blocks in formation]

A FEW chapters on the nature of food, its sources, and the functions it assists to perform in the human system, will very appropriately follow our instructions on the structure and physiology of the digestive system. From a consideration of the latter we must speedily arrive at the conclusion, that the taking and digesting the matter called food is but a process preparatory to other functions. Digestion is, in fact, a process by which substances from without are elaborated and prepared to become part and parcel of the human body. For this purpose the food is first converted into blood, which fluid passes to every organ of the body, and supplies it with the materials necessary for its growth, and the performance of its special functions.

The great cause of the necessity of a constant supply of new matter to the body is the waste of the materials of which the blood and organs are composed, during the performance of their functions. The result of this waste is seen in the form of the various excretions which are thrown off from the body by the skin, liver, kidneys, and bowels. We shall find, then, that the food, the blood, and the excretions, represent each other, that they contain substances of the same nature, and are all com posed of the same ultimate elements.

Before examining the compound substances which are contained in the human body, and which are derived from the food, we shall find it of advantage to study the nature of the elementary principles of which these substances are composed. If we take a portion of human flesh, or blood, and disregard the water, the fat, the fibrine, and other matters it contains, but only seek for its ultimate elements, we shall find that, on accurate analysis, they will yield the following elements:

[subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed]

human body in their pure form, but are combined variously with one another, forming compounds having very different physical properties and chemical relations. These elements may be divided, for physiological purposes, into two classes; the four first, carbon, hydrogen, oxygen, and nitrogen, being balled organic, whilst the remainder are called inorganic elements. The first are called organic elements, because they are found universally present in plants and animals, and because no animal cell and no vegetable cell can grow unless the whole of these elements exist. Hence, as they lie at the foundation of all organic existence, they are properly designated by this term.

The term

The inorganic elements, though very generally present in large classes of animals and plants, are not universal. Man requires phosphorus and calcium in the form of phosphate of lime for his bones; but many of the lower animals contain no phosphate of lime. Sea animals and plants will not live without chlorine and sodium in the form of common salt; but fresh-water plants, and plants away from the sea-shore, do not require this constituent. inorganic, then, is applied to these elements to express their different relation to plants and animals, and will also point out their frequent occurrence in the mineral world. The elements of man's body, however, are all derived from the mineral world, and are identical with the same bodies in inorganic substances. The carbon found in the human body is identical with that which forms, in its pure state, the diamond-which enters into the composition of graphite, and various kinds of coal, and is found in limestone and chalk, forming a part of the carbonic acid of the carbonate of lime, of which these rocks are composed. The hydrogen of the human body is the same as the gas which, united with oxygen, forms water, and when combined with nitrogen produces ammonia. The oxygen of the animal is identical with the gas which, with nitrogen, forms a fifth part of the atmosphere, and which, combined with the metals, forms oxides, of which the greater portion of the earth's surface is composed. The nitrogen of the organic world is identical with that which constitutes so large a portion of the atmosphere. Nor are these elements alone identical in and out of the human body; but we find that they possess the same chemical properties, and that their agency in the human body depends on these properties. Thus, carbon and hydrogen

Few or none of these elements occur in the are inflammable bodies, and have a great

[graphic]
[ocr errors]
[ocr errors]
[ocr errors]

By light," says the Abbé Plo do not mean that semantin which perience in ourselves, un f drave know of any illuminated body, but t to be filled ally able matter which ma ww moim or vibes-pression on the organ of sigh not satisfied in the pfi eve fe ps particles of rice with tilly driven Thin in t

[ocr errors]
[graphic]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]

affinity for oxygen, with which they unite, forming carbonic acid and water, giving out heat during the process of union. This very process goes on in the animal body, and constitutes one of the most important functions of the body. The characteristic features of the functions and properties of animal and vegetable bodies depend on the chemical relations of the four organic elements.

In proceeding, then, with our inquiries into the nature of food, we shall first direct our attention to the organic elements and their compounds, leaving for a while the consideration of the inorganic elements. The first inquiry which needs to occupy us is, "In what forms does the human system obtain its organic elements?" Certainly not in their pure form. Carbon, however needed in the animal frame, cannot be appropriated pure; and a man would starve with the Koh-i-noor diamond in his mouth, were he not allowed to exchange it for more digestible forms of carbon. The gases hydrogen, oxygen, and nitrogen, would, any one of them in their pure state, destroy human life; and even when the two last are mixed in the atmosphere, they will not support life in that form. Again, we may mix them in various ways, and not be more successful. Carbon combines with oxygen to form carbonic acid, and hydrogen combines with nitrogen to form ammonia, and these two compounds unite together to form common smelling-salts, or carbonate of ammonia. But smelling-salts, though they contain all the organic elements, will not serve for human food. Nevertheless what is not food for man is nutriment for plants. Carbonic acid and ammonia supply plants with materials of growth. It is from these two bodies that the vegetable kingdom elaborate all the secretions which give to plants elegance of form, beauty of colour, deliciousness of scent, deadliness as poisons, and nutritiousness as food. The plant stands between the mineral and animal kingdoms, preparing the former for the service of the latter. Without plants there could be no animals. In the whole range of natural history, we are presented with no instance of an animal existing directly on mineral matter. It is true that many animals are carnivorous, and live on the flesh of lower animals. The lion and the tiger prey upon the deer and the antelope; but if we go one step further, we still arrive at the vegetable kingdom as the source of animal nutrition. The deer and the antelope are herbivorous creatures, and the flesh of their body is formed directly

from the plants they eat. So with the animals eaten by man; they are all grain or herb-eating animals, and supply to man the materials they have obtained from the vegetable kingdom. It is on this account that, in speaking of food, we must dwell more at length on the compounds of the organic elements which are found in plants than on those found in animals; for it is in plants they are first formed and prepared for the use of the animal kingdom. Still, were we to seek for some kind of food which should furnish us with a standard by which to judge all other kinds of food, we should not find it amongst plants. To obtain such a standard, we must look to the animal kingdom; and in the food which is supplied to the young of the mammalia, for the first few months of their existence, we find it. As, during the time they are suckling, the young of the mammalia grow rapidly, and all the parts of the body are formed, there must be in milk the representative of the various kinds of substanees which must be taken as food on the one hand, or that form blood on the other.

When human milk is examined, it gives the following results in every 1000 parts: Water Butter Sugar Casein Salts

.......

870

52

63

10

..........

5

1000

These five constituents of milk may be regarded as typical of all kinds of food, whether obtained from the animal or vegetable kingdom. Hence, we may class alimentary substances according as they are represented by one or other of these constituents of milk.

Aqueous. Water is required not only as the medium of conveying the other substances into the body, but it forms a prominent constituent of the body itself. Blood contains 790 parts of water to 210 of solid matter in every 1000. Muscles contain 770 parts of water to 230 solid ingredients. The brain and nerves contain about 800 parts of water in 1000. If food does not contain water naturally, it is taken into the system in the form of tea, coffee, beer, and also in its pure state. quantity of water taken with the food should be about in the proportion of four to one, as we find it in milk. We cannot, however, judge of the quantity contained in solid food till we know its composition. Thus many substances which appear solid contain

The

« FöregåendeFortsätt »