present, when the brain cannot think, and persons sink into a state of unconsciousness. Not only the nervous system, but the muscular system is affected in this way, until at last the starved man is unable to move hand or foot, and dies. Here, then, lies the necessity for the taking of food; the materials of which we are composed are constantly passing away. We are in a state of perennial moult,—I use the word moult intentionally. You know that animals throw off certain parts of their body at certain seasons of the year, and we call that moulting. We apply the term to the periodical casting off of their feathers, hairs, and other epidermal appendages. Crabs and lobsters throw off their shell altogether, birds their feathers, and horses their hair; but in the human being we find this process of moulting is going on constantly-our skin rubs off, our mucous membrane wears away, and our internal organs, all of them, disappear by a similar process, so that I calculate a human being loses about the fortieth part of his weight every day, and in this way you will find that the vital organs of the human body are renewed every forty days. Physiologists formerly supposed that this was a longer process. Taking, for instance, the growth of the hair and nails in certain parts of the body, they supposed that their moulting was the measure of the duration of every part of the body; but if you examine this subject, and calculate the quantity of food we take every day, you will see the period cannot be longer than forty days, in which we take in a bulk of food equivalent to the mass of our bodies, and that this must have passed away in order to make room for the new matters. Thus there is not only a necessity for taking in food which maintains the heat of the body, but there is a necessity for taking the food which maintains the functions of the nervous and muscular systems. Then this waste of which I have been speaking is the result of the activity of our nervous and muscular systems, and the material for its production is supplied, not by the starch, nor by the sugar, nor by the water, nor by the fat which we take as food, but by the substances of which I am now more particularly to speak. There are two sources of this kind of food: the first is the vegetable world, and the second is the animal world. But I shall have to show you here that the vegetable-the plant-is the original source of these substances; for, although we take them from animals, they have first obtained them from plants. Thus the ox and the sheep, which we consume in the form of beef and mutton, have not fed on flesh; they have fed on the grass of the field, on hay, on oats, on peas and beans, on vegetable products, and it is from plants they have derived the flesh which we consume as food. Let us now see what these substances are composed of. I say they are identical in plants and animals,animals deriving them from plants,-and they undergo little or no change when taken into the animal system. We take certain substances from plants and animals, and find that they are identical in composition, and that whether we take them from the plant or the animal is a matter of indifference, provided we digest them and make them into blood. Now the substances which we thus use as food possess considerable chemical interest, and present considerable variations in animals and plants, but I must refer you to chemical manuals for a fuller account of them than I can give here. The three most important forms which they assume in our food are called albumen, fibrine, and caseine. These substances are found in both the animal and vegetable kingdoms. Let us speak first of albumen. Albumen is a substance which is known to exist in the animal kingdom, and we are familiarly acquainted with it as contained in the white of the egg; that is one source of it which is very commonly known, and therefore I speak of it first. And also on this account: that a property which this albumen possesses is well exemplified in the very common process of boiling an egg. You know after you have broken the shell of a boiled egg you get the outside hard and white; now that outside consists of albumen, the inside yellow part called the yolk, also consists principally of albumen, and exhibits the property of coagulating by heat. There are some other places in which albumen is found in the animal system. It is this form of nitrogenous matter which is taken up into the system to form the nervous substance, and with it are formed all those delicate organisms which are called nerves. Nervous matter consists of about 7 per cent. of albumen, not a very large quantity, but still this matter must be regarded by us as an intensely interesting product, because it is the material by which we are put in relation with the external world. It is this which enables us to see, to hear, to taste, to smell, and to feel. It is this which enables us to think, to feel, and to be conscious of our existence. All this depends upon the condition of the albumen in our system. Although we may sit at our breakfast partaking of the daily egg, thinking of other things, yet the laws by which the egg becomes the source of our thought is worth a little consideration. Another source of albumen in the animal kingdom is the blood which circulates through the system of animals. It is composed of water, of albumen, and of fibrine-of water principally. If we say fibrine about one quarter per cent., albumen 7 per cent., globules and salts 13 per cent., and water 80 per cent., you have an approximation to its real composition. From this you will see the importance of albumen. It is the material out of which all our organs are formed. Albumen is not, however, confined to the animal kingdom. I have said all animals must obtain this substance from the vegetable kingdom, and we accordingly find it in plants. Although it is not so often present among plants as fibrine and caseine, yet we find it sufficiently frequent to be able to identify it. It is not, however, necessary to supply this substance in its pure form in order to have it deposited in the body. In the stomach there is a power of converting caseine and fibrine into albumen. The albumen that is introduced into the stomach is cooked, deprived, as it were, of the vital property, and therefore it has to be revitalised, made again into albumen and a living substance, and it is then that it is taken up into the blood. It is the same with fibrine and caseine. Then, I say, there are some plants which contain albumen. Here I have a series of analyses containing the quantities of the flesh-forming matters, the produce of various kinds of food, and you will find that some of them contain albumen. |