substances, such as water, starch, sugar, glucose, oil, vegetable acids, albuminoids, etc., and the character of any given food, its value, etc., depends upon the proportion in which these various substances are found. I may, perhaps, illustrate this by giving the composition of two fodders well known, first stating, however, that the composition here given is the total composition, and not the digestible matter which will be spoken of later. I have selected two foods of very different composition, to show more clearly the idea that the proportion in which the various parts exist has much to do with the value per cent.

The following table shows the percentage composition of corn. meal and southern corn ensilage:

The above table presents a complete analysis, but in the practical tables for stock feeding, the starch, sugar, fiber, and gum are included under the general term carbo-hydrates, and by condensing these we get the following:

The value of any food depends, of course, upon its dry substance, that is, the water of the food need not ordinarily be considered, as the animal will make up at the trough what is lacking in the food, although there is a question as to this which I shall speak of again. Corn meal in 100 pounds has 88 pounds of dry matter, while 100 pounds of ensilage has only 20.42 ; that is, corn meal has 43 times as much total food matter in it as ensilage. Well-cured English hay has not far from 12 per cent of water in it; roots average 80 per cent of water; cottonseed meal has per cent; gluten meal, 10.5 per cent, etc.

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There is another thing which affects the value of a fodder more than its total per cent of dry matter. It is the ratio existing between the albuminoids and the non-albuminoids or carbo-hydrates and fat, but before we consider this it will be best to take up the matter of digestibility of food.

DIGESTIBILITY OF FOOD.

The composition of food has been given with a view of showing in general that vegetable matter consists of albuminoids, or substances resembling the whites of eggs, carbohydrates, or starch, sugar, gum, etc., and fats or oils, which in many cases constitute a large per cent of seeds, e. g., in cottonseed, linseed, etc.; but while the chemist can give us the total composition of any given vegetable product, he cannot, in his laboratory, tell how much of this is available to the animal. This link in our chain must be forged by the physiological chemist.

When we feed to our cows or oxen a hundred weight of the corn meal, the analysis of which was given above, we are not feeding ten pounds of available albuminoids and seventy-one and nine-tenths pounds of available carbo-hydrate, because a part of this materal goes through the system unchanged, and hence has no nutritive effect. We may illustrate this by calling to mind a ton of a mixture of coal and gravel stones, for example. Suppose that fifteen hundred pounds of the best stove coal is mixed with five hundred pounds of stones, and we use the mixture for

fuel, it is evident that the fuel value of the whole would be only that of the fifteen hundred pounds, because that alone would burn in the stove. In just the same way the albuminoids, carbohydrate, and fat in the corn meal are made up of two parts, one digestibles and the other indigestible. The former, being consumed in the system, helps to maintain life, and is the true source of value to the food so far as the animal is concerned, corresponding with the coal in our illustration. The undigested materials take no part in the maintenance of life, and are to the whole food what the stone is to our mixed fuel. Now if we were buying a mixture of coal and stone with which to feed our stove, we should pay only in proportion to the actual coal present, and if we are to buy food materials for our farm animals, or to raise the same, we ought to value them not in proportion to their total composition but to the available or digestible portion of the various substances of the food, and to this available part the term NUTRIENTS has been applied.

The method of determining the digestibility of the several constituents of food is briefly as follows: An animal is placed in a tight stall where no loss can take place, the food consumed is weighed, and samples analyzed, and the solid excrement is also weighed and analyzed. The difference in amount of each substance taken into the system and the amount of the same voided in the manure shows the part digested. albuminoids were digested none would excrement, or at least but a small amount. if one half as much appears in the manure as was contained in the food consumed, then fifty per cent of the total albuminoids of the food was digested. This, of course, is the general way of determining the nutrients in a food, but many precautions are taken and various ways devised to check the work and elimi

nate errors.

Thus if all of the appear in the solid On the other hand,

Thus far, then, we have seen that foods are made up of unlike parts, that only a portion of each material contained in a given food is digestible or available to the animal, and we have seen how the investigator determines the per cent of digestibility by feeding and analysis. We will next illustrate and inforce the idea by a few examples.

Experiments with the horse show that, on an average, seventyeight per cent of the albuminoids are digestible, sixty-three per cent of the fat, and ninety-five per cent of the carbo-hydrates. Applying these figures to the corn meal, the analysis of which has been given, we get the following table, which shows first, total composition, second, per cent of digestibility, and third, the amount of digestible material in one hundred pounds.

That is, out of eighty-eight pounds of dry matter about eighty pounds are available, or true nutrients, capable of supporting animal life, producing beef, pork, milk, wool, or muscular force.

The course of digestion is in brief as follows: In the mouth the food is crushed and mixed with saliva, a juice capable of changing starch into sugar; in cud-chewing animals (ruminants) the food is again brought to the mouth and reground and mixed, passing indirectly from the mouth into the fourth or true stomach, where the digestion proper commences. In this stomach the gastric juice is formed, and by its action the insoluble albuminoids are made soluble, and thus rendered available to the animal. After the food passes from the stomach, it is mixed with bile or gall, and with the pancreatic juice, the former acting on the fat of the food and the latter upon the starch and albuminoids. The following recapitulation, taken from Armsby, will give a concise view of the whole process: "We see, then, that the whole process of digestion is simply a conversion of the solid matters of the food into forms which are

soluble in water or in the digestive fluids, and can, therefore, pass into the circulation. This is accomplished in case of the albuminoids by the gastric juice in the stomach and the pancreatic juice in the intestines, in case of starch, etc., by the saliva and pancreatic juice, and in the case of the fats by the bile and pancreatic juice."

The next subject which comes in the natural course of events is the use to which food is put in the animal system, how the various parts act, what is the function of the albuminoids, the carbo-hydrates, and the fats, and in connection with it the composition of the animal body must be considered.

USES OF FOOD.

The body of an animal is made up of various materials; there is the fat, the lean or muscle, the bone, the hair, the "cords" or tendons, etc., and each of these parts varies in chemical composition. Now, if we start with a calf weighing one hundred pounds, and produce from that calf an ox weighing fifteen hundred pounds, we must add to the one hundred pounds fourteen hundred pounds, and this must come from the food and drink given the animal; hence it may be well to show in tabular form the exact amount of the various constituents in both the calf and ox, and see how these vary.

It is easy then to see that one use of the food consumed must be to furnish fat, albuminoids, and ash with which to build up this increase of live weight, but if this were all, the question of stock feeding would be a very simple one.