OF TEN

THE object I have in view in this course of Lectures is to bring under notice the principal forms of those subtances of which we partake, from day to day, under the name of Food; by means of which we live, and without which we should die. The life of man is like a fire. Just as the fire must have fuel in order that it may burn, so we must have food in order that we may live; and the analogy is in many respects quite correct; for we find that man really produces in his body a certain amount of heat, just as the fire does, and the result of the combustion of the materials of his food is the same as the result of burning fuel in a fire. Man, in fact, exists in consequence of the physical and chemical changes that go on in his body as the result of taking food.

One of the most important results of the taking of food is that the human body, which is destroyed from day to day by the processes and the wear and tear of life, is kept up and maintained at a given bulk. Thus, we find, if we take, for instance, a man weighing 154 lbs., that he would lose in the course of a day from three to four pounds of matter by the various vital processes of his body. Now this matter must be remain the same. Then,

supplied in order that he again, man's body is maintained at a given temperature. If we take a thermometer, and put it under the tongue, and compare it with the atmospheric temperature, there is usually a difference. The thermometer will stand at 98° in the human body, whatever may be the external temperature; and this is the result of a certain quantity of food being consumed in the system. Our food, then, first nourishes the body; and, secondly, maintains its heat. We shall find, however, that although these are the principal processes that go on, they are attended with others connected with the suppply of food. I have here drawn up a table, as a kind of classification of food.

CLASSIFICATION OF FOOD.

CLASS I.-ALIMENTARY OR NECESSARY FOOD.

Group 1.-MINERAL :

Water; Salt; Ashes of Plants and Animals.

Group 2.-CARBONACEOUS-FORCE AND HEAT-GIVING:Starch; Sugar; Fat.

Group 3.-NITROGENOUS OR

NUTRITIOUS-FLESH

FORMING :-Albumen; Fibrine; Caseine.

CLASS II.-MEDICINAL OR AUXILIARY FOOD.

Group 4.-STIMULANTS:-Alcohol; Volatile Oils.

Group 5.-NEUROTICS:-Alkaloids.

Group 6.-NARCOTICS:-Tobacco; Hemp; Opium.

CLASS III.-ACCESSORY FOOD.

Group 7.-Cellulose; Gum; Gelatine.

There

You will see that food is divided into two great groups;-into that which is necessary from day to day, and without which we could not live, and that which acts rather as a medicine or as an auxiliary. is also a third group, which may be regarded as accessory foods. Taking the first group of dietetical substances, we come to water. We cannot do without water; we must drink; and thus it becomes a necessary of life. Most of the other substances in this group are necessarily taken from day to day. Then, in the auxiliary group you will see spirits, wine, and beer: they are not absolutely necessary to life; many persons live without them. Then we have tea, coffee, and cocoa-they are auxiliaries; and so on with the other substances mentioned in this part of our table. I call these substances medicinal, because they act on the system as medicines. We take alcohol as food, just as we administer sal volatile, camphor, and other drugs as medicines. Medicine and food are more allied to each other than most persons think; and medicines are constantly administered from a dietetical point of view.

In the present course of six lectures, I propose to treat of the group of the alimentary, or necessary sub

stances of our food. I have divided these groups into seven, and you will see the first group is more nearly allied to the third than to the second; but taking the first, we find that water constitutes the basis of all the beverages we take from day to day. When we take beer, we take a large quantity of water; when we take tea or coffee, we take water. Then there are certain mineral substances which are necessary to form the fabric of our bodies. If we take an animal body and analyze it, we find that there are certain incombustible matters in that body-ashes as we call them. These constitute our mineral food. Then there is the group, consisting of substances taken for the purpose of giving force and maintaining animal heat-such as starch and sugar; they are necessary, inasmuch as they act upon the animal system by coming in contact with the oxygen of the air, and give out heat; so we call them combustible. These substances will supply us with material for our first four lectures. We then come to the nutritious group, which constitutes the flesh-forming substances of our food. These are necessary for forming the muscles and nerves of our body.

I now commence with water. Water, in many respects, more closely resembles nutritive food than it does force-giving food; that is to say, it more closely approaches, in its relation to the human system, the character of flesh than it does the character of starch or sugar; and for this reason, that it combines with the tissues of the body, and forms a necessary part of its

structure.

I have made a calculation that a human body

You

weighing 154 lbs. contains 111 lbs. of water. see, then, how necessary water is. If you reduce the size of the man, you reduce the quantity of water; and you will find that water enters into the composition of all our food.

Before speaking more particularly of water, I will call your attention, in the first place, to its composition: it is not my province to dwell on the elementary composition of food any further than it throws a light on its action. Water, then, is composed of two gases, one called oxygen, and another called hydrogen; and we can easily decompose water so as to demonstrate its composition. If you take a piece of potassium, which is a metal so malleable that you can cut it with a knife, and put it into water, it has such an affinity for the oxygen of the water, that when combined with it, it inflames. On putting it into water, the metal actually appears to take fire, and is converted into common potash. The hydrogen gas of the water is liberated, and it is this gas which burns during the decomposition of the water. This is a beautiful chemical experiment, and demonstrates the composition of water. there are many other ways of doing this. If we take a little alcohol, or anything which contains hydrogen, and burn it in atmospheric air, under a glass vessel, we shall find that we produce water; so that we can easily by household experiments demonstrate the composition of water.

But

I now come to speak of water in relation to the life of plants and animals. Both animals and plants require it; and no animal, and no plant, exists without certain quantities of water. Sometimes it is so large in