The _second cla.s.s_ of proximates, though forming only a small part of the plant, are of the greatest importance to the farmer, being the ones from which _animal muscle_[H] is made. They consist, as will be recollected, of carbon, hydrogen, oxygen and _nitrogen_, or of _all_ of the organic elements of plants. They are all of much the same character, though each kind of plant has its peculiar form of this substance, which is known under the general name of _protein_.

The protein of wheat is called _gluten_--that of Indian corn is _zein_--that of beans and peas is _legumin_. In other plants the protein substances are _vegetable alb.u.men_, _casein_, etc.

Gluten absorbs large quant.i.ties of water, which causes it to swell to a great size, and become full of holes. Flour which contains much gluten, makes light, porous bread, and is preferred by bakers, because it absorbs so large an amount of water.

[What is the result if a field be deficient in nitrogen?]

The protein substances are necessary to animal and vegetable life, and none of our cultivated plants will attain maturity (complete their growth), unless allowed the materials required for forming this const.i.tuent. To furnish this condition is the object of nitrogen given to plants as manure. If no _nitrogen_ is supplied the protein substances cannot be formed, and the plant must cease to grow.

When on the contrary _ammonia_ is given to the soil (by rains or otherwise), it furnishes nitrogen, while the carbonic acid and water yield the other const.i.tuents of protein, and a healthy growth continues, provided that the soil contains the _mineral_ matters required in the formation of the ash, in a condition to be useful.

The wisdom of this provision is evident when we recollect that the protein substances are necessary to the formation of muscle in animals, for if plants were allowed to complete their growth without a supply of this ingredient, our grain and hay might not be sufficiently well supplied with it to keep our oxen and horses in working condition, while under the existing law plants must be of nearly a uniform quality (in this respect), and if a field is short of nitrogen, its crop will not be large, and of a very poor quality, but the soil will produce good plants as long as the nitrogen lasts, and then the growth must cease.[I]

ANIMALS.

That this principle may be clearly understood, it may be well to explain more fully the application of the proximate const.i.tuents of plants in feeding animals.

[Of what are the bodies of animals composed?

What is the office of vegetation?

What part of the animal is formed from the first cla.s.s of proximates?

From the second?

Which contains the largest portions of inorganic matter, plants or animals?

Must animals have a variety of food, and why?]

Animals are composed (like plants) of organic and inorganic matter, and every thing necessary to build them up exists in plants. It seems to be the office of the vegetable world to prepare the gases in the atmosphere, and the minerals in the earth for the uses of animal life, and to effect this plants put these gases and minerals together in the form of the various _proximates_ (or compound substances) which we have just described.

In animals the compounds containing _no nitrogen_ comprise the fatty substances, parts of the blood, etc., while the protein compound, or those which _do contain nitrogen_, form the muscle, a part of the bones, the hair, and other portions of the animal.

Animals contain a larger proportion of inorganic matter than plants do.

Bones contain a large quant.i.ty of phosphate of lime, and we find other inorganic materials performing important offices in the system.

In order that animals may be perfectly developed, they must of course receive as food all of the materials required to form their bodies. They cannot live if fed entirely on one ingredient. Thus, if _starch_ alone be eaten by the animal, he might become _fat_, but his strength would soon fail, because his food contains nothing to keep up the vigor of his _muscles_. If on the contrary the food of an animal consisted entirely of _gluten_, he might be very strong from a superior development of muscle, but would not be fat. Hence we see that in order to keep up the proper proportion of both fat and muscle in our animals (or in ourselves), the food must be such as contains a proper proportion of the two kinds of proximates.

[Why is grain good for food?

On what does the value of flour depend?

Is there any relation between the ashy part of plants and those of animals?

How may we account for unhealthy bones and teeth?]

It is for this reason that grain, such as wheat for instance, is so good for food. It contains both cla.s.ses of proximates, and furnishes material for the formation of both fat and muscle. The value of _flour_ depends very much on the manner in which it is manufactured. This will be soon explained.

[What is a probable cause of consumption?

What is an important use of the first cla.s.s of proximates?

What may lungs be called?

Explain the production of heat during decomposition.

Why is the heat produced by decay not perceptible?]

Apart from the relations between the _proximate principles_ of plants, and those of animals, there exists an important relation between their _ashy_ or _inorganic_ parts; and, food in order to satisfy the demands of animal life, must contain the mineral matter required for the purposes of that life. Take bones for instance. If phosphate of lime is not always supplied in sufficient quant.i.ties by food, animals are prevented from the formation of healthy bones. This is particularly to be noticed in teeth. Where food is deficient of phosphate of lime, we see poor teeth as a result. Some physicians have supposed that one of the causes of consumption is the deficiency of phosphate of lime in food.

[Why is the heat produced by combustion apparent?

Explain the production of heat in the lungs of animals?

Why does exercise augment the animal heat?

Under what circ.u.mstances is the animal's own fat used in the production of heat?]

The first cla.s.s of proximates (starch, sugar, gum, etc.), perform an important office in the animal economy aside from their use in making fat.

They const.i.tute the _fuel_ which supplies the animal's fire, and gives him his _heat_. The lungs of men and other animals may be called delicate _stoves_, which supply the whole body with heat. But let us explain this matter more fully. If wood, starch, gum, or sugar, be burned in a stove, they produce heat. These substances consist, as will be recollected, of carbon, hydrogen, and oxygen, and when they are destroyed in any way (provided they be exposed to the atmosphere), the hydrogen and oxygen unite and form water, and the carbon unites with the oxygen of the air and forms carbonic acid, as was explained in a preceding chapter. This process is always accompanied by the liberation of _heat_, and the _intensity_ of this heat depends on the _time_ occupied in its _production_. In the case of decay, the chemical changes take place so slowly that the heat, being conducted away as soon as formed, is not perceptible to our senses. In combustion (or burning) the same changes take place with much greater rapidity, and the same _amount_ of heat being concentrated, or brought out in a far shorter time, it becomes intense, and therefore apparent. In the lungs of animals the same law holds true. The blood contains matters belonging to this carbonaceous cla.s.s, and they undergo in the lungs the changes which have been described under the head of combustion and decay.

Their hydrogen and oxygen unite, and form the moisture of the breath, while their carbon is combined with the oxygen of the air drawn into the lungs, and is thrown out as carbonic acid. The same consequence--heat--results in this, as in the other cases, and this heat is produced with sufficient rapidity for the animal necessities. When an animal exercises violently, his blood circulates with increased rapidity, thus carrying carbon more rapidly to the lungs. The breath also becomes quicker, thus supplying increased quant.i.ties of oxygen. In this way the decomposition becomes more rapid, and the animal is heated in proportion.

Thus we see that food has another function besides that of forming animal matter, namely to supply heat. When the food does not contain a sufficient quant.i.ty of starch, sugar, etc., to answer the demands of the system the _animal's own fat_ is carried to the lungs, and there used in the production of heat. This important fact will be referred to again.

FOOTNOTES:

[G] By _proximate principle_, we mean that combination of vegetable elements which is known as a vegetable product, such as _wood_, etc.

[H] _Muscle_ is _lean meat_, it gives to animals their strength and ability to perform labor.

[I] This, of course, supposes that the soil is fertile in other respects.

CHAPTER VII.

LOCATION OF THE PROXIMATES AND VARIATIONS IN THE ASHES OF PLANTS.

[Of what proximate are plants chiefly composed?

What is the princ.i.p.al const.i.tuent of the potato root?

Of the carrot and turnip?

What part of the plant contains usually the most nutriment?]