we may know of what they consist, we must refer to the composition of food and examine the process of digestion. The food of animals, we have seen to consist of both organic and inorganic matter. The organic part may be divided into two classes, i. e., that portion which contains nitrogen-such as gluten, albumen, etc., and that which does not contain nitrogen -such as starch, sugar, oil, etc. The inorganic part of food may also be divided into soluble matter and insoluble matter. DIGESTION AND ITS PRODUCTS. Let us now suppose that we have a full-grown ox, which is not increasing in any of his parts, but only consumes food to keep up his respiration, and to supply the natural wastes of his body. To this ox we will feed a ton of hay which contains organic matter, with and without nitrogen, and soluble and insoluble inorganic substances. Now let us try to follow it through its changes in the animal, and observe its destination. Liebig compares the consumption of food by animals to the imperfect burning of wood in a stove, where a portion of the fuel is resolved into gases and ashes (that is, it is completely burned), and Of what is animal excrement composed? Explain the composition of the food of animals. What does hay contain? To what does Liebig compare the consumption of food by animals, and why? another portion, which is not thoroughly burned, passes off as soot. In the animal action in question, the food undergoes changes which are similar to this burning of wood. A part of the food is digested and taken up by the blood, while another portion remains undigested, and passes the bowels as solid dungcorresponding to soot. This part of the dung then, we see is merely so much of the food as passes through the system without being materially changed. Its nature is easily understood. It contains organic and inorganic matter in nearly the same condition as they existed in the hay. They have been rendered finer and softer, but their chemical character is not materially altered. The dung also contains small quantities of nitrogenous matter, which leaked out, as it were, from the stomach and intestines. The digested food, however, undergoes further changes which affect its character, and it escapes from the body in three ways-i. e., through the lungs, through the bladder, and through the bowels. It will be recollected from the first section of this book, p. 22, that the carbon in the blood of animals, unites with the oxygen of the air drawn into the lungs, and is thrown off in the breath as carbonic acid. The hydrogen and oxygen unite to form a part of the water which constitutes the moisture of the breath. Of what does that part of dung consist which resembles soot? What else does the dung contain? In what manner does the digested part of food escape from the body! That portion of the organic part of the hay which has been taken up by the blood of the ox, and which does not contain nitrogen (corresponding to the first class of proximates, as described in Sect. I), is emitted through the lungs. It consists, as will be recollected, of carbon, hydrogen and oxygen, and these assume, in respiration, the form of carbonic acid and water. The organic matter of the digested hay, in the blood, which contains nitrogen (corresponding to the second class of proximates, described in Sect. I), goes to the bladder, where it assumes the form of urea a constituent of urine or liquid manure. We have now disposed of the imperfectly digested food (dung), and of the organic matter which was taken up by the blood. All that remains to be examined is the inorganic or mineral matter in the blood, which would have become ashes, if the hay had been burned. The soluble part of this inorganic matter passes into the bladder, and forms the inorganic part of urine. The insoluble part passes the bowels, in connection with the dung. If any of the food taken up by the blood is not returned as above stated, it goes to form fat, muscle, hair, bones, or some other part of the animal, and as Explain the escape of carbon, hydrogen and oxygen. How is the soluble ash of the digested food parted with If any portions of the food are not returned in the dung, how are they disposed of! he is not growing (not increasing in weight) an equivalent amount of the body of the animal goes to the manure to take the place of the part retained.* We now have our subject in a form to be readily understood. We learn that when food is given to animals it is not put out of existence, but is merely changed in form; and that in the impurities of the breath, we have a large portion of those parts of the food which plants obtain from air and from water; while the solid and liquid excrements contain all that was taken by the plants from the soil and manures. The SOLID DUNG contains the undigested parts of the "LIQUID MANURE " food, the insoluble parts of the ash, and the nitrogenous matters which have escaped from the digestive organs. the nitrogenous or second class of proximates of the digested food, and the soluble parts of the ash. * This account of digestion is not, perhaps, strictly accurate in a physiological point of view, but it is sufficiently so to give an elementary understanding of the character of excrements as manures. How is their place supplied! Is food put out of existence when it is fed to animals? What does the solid dung contain? Liquid manure? The breath! The BREATH contains the first class of proximates, those which contain carbon, hydrogen and oxygen, but no nitrogen.* CHAPTER III. WASTE OF MANURE. THE loss of manure is a subject which demands most serious attention. Until within a few years, little was known about the true character of manures, and consequently, of the importance of protecting them against loss. The first causes of waste are evaporation and leaching. EVAPORATION. Evaporation is the changing of a solid or liquid body to a vapory form. Thus common smelling salts, a solid, if left exposed, passes into the atmosphere in * The excrements of animals contain more or less of sulphur, and sometimes small quantities of phosphorus. What are the first causes of loss of manure? |