down by a burden of tempting fruit. Autumn will succeed, to stop the growth and give a new colour to its leaves; and chill winter will strip it of all its leafy pride, and leave it naked as when spring time began.

Such is the yearly plant-life, as seen by the ordinary cultivator, or watched with daily care by the lover of vegetable nature. But, beneath this outer open life, there is an inner secret life which the common eye does not see. A constant invisible intercourse has all the time been taking place between the external air and the most hidden parts of the internal plant. No sooner does the little leaf burst the swelling bud, than a thousand unseen mouths open on its surface to suck in the airy food which now for the first time comes within their reach. These minute mouths (stomata) are scattered in millions over the leaf, now on its upper, now on its under side, and now on both, according to the circumstances in which the plant is destined to live. Beginning with the first dawn of sunlight, they perpetually suck in carbonic acid from the atmosphere, and give off oxygen gas in nearly equal volume, till the sun goes down. Then, with a view to other chemical ends, and, obedient to the retiring sun, they change the nature of their work. While darkness lasts, they take back carbonic acid from the air, and give out again pure oxygen gas. And thus, day after day, the leafy labour proceeds, and by the aid of the raw materials which the working mouths thus incessantly carry out and in, other vital parts within the plant produce the varied forms of matter of which the vegetable substance consists. The solid stem is formed, as it were, of compressed and hardened air; and vast forests on a thousand hills thus steal from the atmosphere the carbonaceous matter of which they mainly consist.

But a marvel of wondrous forethought discloses itself as we interrogate more nearly this mutual relation between terrestrial plant-life and the air which surrounds it. The quantity of carbon in the air, as we have seen, is small; some thirty odd grains over every square inch. The active growth of vegetable matter over the entire surface of the globe, is able to convert the whole of this carbon into the substance of solid wood within the lifetime of a single generation of men. But hundreds of generations of men have already lived on the earth, and thousands of generations of other animals before him, yet carbon is as abundant in the atmosphere as ever, and vegetable growth, in similar circumstances, quite as luxuriant. There must, therefore, be some natural sources of supply from which carbonic acid gas flows into the air, as fast as the leafy mouths

withdraw it. These sources, also, must be watched and regulated, that they may not pour it in so fast as to increase unduly the natural proportion of this poisonous gas in an atmosphere which man and countless other animals perpetually breathe. These several conditions are beautifully fulfilled by a series of compensating natural operations, which, like the growth of plants, form a part of the existing system of things; and, like it, never cease to proceed at a duly measured pace.

Thus, plants die, and the carbon of their stems and leaves is gradually resolved again into carbonic acid by the gradual progress of decay, or by the quicker agency of fire. Or the plant is eaten by the living animal, and after many chemical changes within the animal's body, its carbon is breathed forth again from the lungs and skin in the form of carbonic acid. In these several ways the very same carbon which the plant-leaf has taken from the air, is again, in a great measure, returned to it. A certain small and indefinite proportion of their carbon is indeed yearly buried in the soil, or covered up in the depths of the sea, or accumulated in bogs and dismal swamps. But to make up for this, the earth itself, from bubbling springs, from myriads of unseen fissures, and from the open mouths of many volcanoes pours forth a ceaseless contribution of carbonic acid gas, ceaseless, yet in such wise limited, that so long as vegetation lasts, it cannot render the atmosphere unwholesome to animal life. To the knowledge of these and many similar adjustments, the study of the chemistry of the air we breathe has gradually led us.

Turn now to the water we drink. In this admirable fluid, so clear, so bright, so grateful to the system, so healthful to the temperate, so necessary to all, the delight of Grecian song,the charm of the Eastern paradise, of this fluid, lauded with justice by the physiologist, and worshipped, not unduly, by the total abstainer,chemistry tells us that three-fourths of our apparently solid bodies consist, and that it forms nearly as large a proportion of all living vegetables during the height and vigour of their growth. In this fluid, looked upon as elementary till nearly our own times, modern research has taught us to see the result of a subtle union between the oxygen we have spoken of, and another gas, to which the name of hydrogen (water-former) has been given. Kindle this latter gas in the air, and it burns with a pale flame. Hold a cold bell glass over the flame, and its under surface will become bedewed with moisture, and drops of water will trickle down its sides. Collect this water and submit it to a current of electricity; the liquid will disappear, and in its stead the two gases

oxygen and hydrogen will remain. These experiments prove, first, that while burning in the air, the hydrogen unites with the oxygen of the atmosphere and forms water; and, second, that the water thus formed consists of these two gaseous constituents only, compressed and bound together by some incomprehensible connexion which it makes us no wiser to call chemical combination.

It is, indeed, incomprehensible how water, the enemy of fire, should itself consist of two gases, the one of which burns most readily, while the other is the great natural supporter of living fire. And it is equally strange that oxygen, so indispensable to animal life, should form eight-ninths by weight of a liquid in which few terrestrial animals can live for more than two or three seconds of time. By no known theory of physical or mechanical union can we satisfactorily explain how properties so new should be the result of such chemical combinations.

The most

The chemical study of this water in its relations to animal and vegetable life presents new points of interest. important of its chemical properties are so familiar to us that we rarely think of them, and certainly do not sufficiently prize them. Pure water has neither taste, nor smell, nor pungency. It is neither sour like vinegar, nor sweet like sugar, nor alkaline like soda. It irritates no nerve of sensation, even the most delicate, nor is the tenderest part of the animal frame disturbed by contact with this universal fluid. It is thus fitted to penetrate unfelt into the subtlest tissues, and without causing the slightest jar to flow along the finest, most sensitive, and most hair-like vessels. It soothes and assuages wherever it comes, lessening inflammation, lulling pain, diluting unhealthy fluids within the body, and washing morbid humours and waste materials from the sickly and changing frame.

Again, as a cooling agent water is equally invaluable. In a dry and thirsty land we feel and acknowledge the pleasure of bathing our heated bodies in the sea or the running stream. But we are less sensible how it watches over us, as it were, every passing moment, dispelling each rising heat, and removing from the body every excess of warmth which might disturb the equable working of its many parts. Do we eat inflammatory food, or drink over-stimulating fluids, the excess of bodily warmth produced converts a portion of water into vapour, and the lungs throw it off into the air. Do we by hard labour, or other unusual exertion, exalt the temperature of the body, the same water again takes up the superfluous heat, and bathing with perspiration both skin and lungs restrains within due bounds the growing inflammation.

But more widely useful still in relation to vegetable and animal life is the property which water possesses of dissolving and rendering fluid a host of usually solid bodies. Put sugar or salt into water, it disappears and becomes fluid and penetrative like the water itself. The salt sea contains within its bosom many substances so dissolved; the fluids that circulate through our veins are chiefly water holding various compound bodies in solution; the moisture which the plant-root drinks in carries with it into root, stem, and leaf many substances it has taken up from the soil; and the purest waters we consume for domestic use are not free from foreign matters of mineral and organic origin. In all this there is a purpose, and good flows to all living things from this solvent power of water.

It must suffice at present to mention one general benefit. Into the composition of the plant a variety of solid mineral substances enter, which it is the duty of the plant root to draw from the soil. In their solid form these substances could neither move freely through the soil nor find their way into the fine pores of the little rootlets. But dissolved in water they move as freely as the liquid itself, and penetrate with it into the most delicate tissues of plant or animal. Thus along the finest vessels they ascend through stem and twig and leaf, and distribute themselves wherever their presence is required.

It is so also with the animal. Into all its parts, solid saline, and mineral, matters enter as a necessary portion of their substance. These we introduce into the stomach along with our other food, but water must dissolve them there and make them fluid before they can find their way into the blood and be afterwards conveyed to the parts of the body where their several services are required. And here comes into view a glimpse of wise beneficence in what at first sight appears only a form of material evil. The impurities, as we call them, of natural waters are often of real advantage to those who drink them, supplying saline and mineral matters in which the food is deficient, or which the peculiar nature of the staple form of diet in a given region renders grateful to the enfeebled frame. The purest waters, therefore, are by no means to be considered as everywhere and in all cases the most wholesome. The natural waters of every locality are more or less medicated, so to speak, and the constitutions of the inhabitants by long use become adapted to their peculiar quality, and even their food is adjusted to it; so that to change their wonted beverage even for one more pure may sensibly affect the health, for years to come, of large masses of people.

Look next at the food we eat. This is either of vegetable or

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of animal origin, and what modern chemistry tells us regarding it is not only full of rich uses and of deep personal interest to every one of us, but is in itself truly marvellous. For, first, it abolishes the artificial distinction which mere sense has long established between animal food and vegetable food. The bread we simply bake is no longer quite different in use and quality from the flesh meats on which learned cooks exhaust their culinary skill. In bread we actually eat the substance of beef, and in bread and butter another form of that marbled flesh on which the eye of the epicure so placidly rests. In every variety of eatable plant there exists a proportion of what chemists call gluten, which is nearly identical with the muscular part of animal flesh, and a proportion also of fat, which is absolutely identical with the fat of animals. How unphilosophical and vain, therefore, the discipline which enjoins and makes a merit of abstaining from a substance when obtained from the body of an animal, and yet allows the use of the same substance when obtained from a vegetable!

Again, it shows us how curiously and by what admirable contrivances this food is prepared for man. Of carbon and nitrogen, such as float in the air, combined with the oxygen and hydrogen gases already spoken of, the flesh and tissues of animals, and the solid portions of vegetables in great part consist. But of these only one, the oxygen, serves directly as food either to animal or to plant. The plant, as we have seen, sucks in at times oxygen by its leaves, and some of this oxygen, no doubt, contributes to the formation of its growing substance. The animal, also, draws in oxygen from the air by its lungs, and uses it directly to build up the tissues of its body. Thus both animals and plants, to a certain small extent, feed upon raw and unchanged oxygen. But neither plant nor animal can so consume or work up elementary or uncombined hydrogen, nitrogen, or carbon.

And here, in pursuing further our inquiries in regard to the way in which they are respectively fed, a great difference at once presents itself between the plant and the animal; while, at the same time, a close and predetermined relation is seen evidently to exist between them.

It would be out of place here minutely to discuss the way in which plants and animals are nourished and sustained. It is sufficient to observe, that throughout what may be called dead or mineral nature there exist numerous, more or less simple, compounds of hydrogen, carbon, and nitrogen, which the plant is able to appropriate and employ in building up its growing