What becomes of the nitrogenous parts?

How is the _soluble_ ash of the digested food parted with?

The insoluble?

If any portions of the food are not returned in the dung, how are they disposed of?]

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_ cla.s.s 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 a.s.sume, 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_ cla.s.s of proximates, described in Sect. I), goes to the _bladder_, where it a.s.sumes the form of urea--a const.i.tuent 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 pa.s.ses into the bladder, and forms the _inorganic part of urine_. The _insoluble_ part pa.s.ses the bowels, in connection with the dung.

[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?]

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 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.[V]

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 food, the _insoluble_ parts of the ash, and the nitrogenous matters which have _escaped_ from the digestive organs.

"LIQUID MANURE" the nitrogenous or _second cla.s.s_ of proximates of the digested food, and the _soluble_ parts of the ash.

THE BREATH contains the _first cla.s.s_ of proximates, those which contain carbon, hydrogen and oxygen, but _no nitrogen_.[W]

FOOTNOTES:

[V] 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.

[W] The excrements of animals contain more or less of sulphur, and sometimes small quant.i.ties of phosphorus.

CHAPTER III.

WASTE OF MANURE.

[What are the first causes of loss of manure?

What is _evaporation_?]

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.

[Name a solid body which evaporates.

What takes place when a dead animal is exposed to the atmosphere for a sufficient time?

What often a.s.sist the evaporation of solids?]

Evaporation is the changing of a solid or liquid body to a vapory form.

Thus common smelling salts, a solid, if left exposed, pa.s.ses into the atmosphere in the form of a gas or vapor. Water, a liquid, evaporates, and becomes a vapor in the atmosphere. This is the case with very many substances, and in organic nature, both solid and liquid, they are liable to a.s.sume a gaseous form, and become mixed with the atmosphere.

They are not destroyed, but are merely changed in form.

As an instance of this action, suppose an animal to die and to decay on the surface of the earth. After a time, the flesh will entirely disappear, but is not lost. It no longer exists as the flesh of an animal, but its carbon, hydrogen, oxygen, and nitrogen, still exist in the air. They have been liberated from the attractions which held them together, and have pa.s.sed away; but (as we already know from what has been said in a former section) they are ready to be again taken up by plants, and pressed into the service of life.

The evaporation of liquids may take place without the aid of any thing but heat; still, in the case of solids, it is often a.s.sisted by decay and combustion, which break up the bonds that hold the const.i.tuents of bodies together, and thus enable them to return to the atmosphere, from which they were originally derived.

[What is the cause of odor?

When we perceive an odor, what is taking place?

Why do manures give off offensive odors?

How may we detect ammonia escaping from manure?]

It must be recollected that every thing, which has an _odor_ (or can be smelled), is evaporating. The odor is caused by parts of the body floating in the air, and acting on the nerves of the nose. This is an invariable rule; and, when we perceive an odor, we may be sure that parts of the material, from which it emanates, are escaping. If we perceive the odor of an apple, it is because parts of the volatile oils of the apple enter the nose. The same is true when we smell hartshorn, cologne, etc.

Manures made by animals have an offensive odor, simply because volatile parts of the manure escape into the air, and are therefore made perceptible. All organic parts in turn become volatile, a.s.suming a gaseous form as they decompose.

We do not see the gases rising, but there are many ways by which we can detect them. If we wave a feather over a manure heap, from which ammonia is escaping, the feather having been recently dipped in manure, white fumes will appear around the feather, being the muriate of ammonia formed by the union of the escaping gas with the muriatic acid. Not only ammonia, but also carbonic acid, and other gases which are useful to vegetation escape, and are given to the winds. Indeed it may be stated in few words that all of the organic part of _plants_ (all that was obtained from the air, water, and ammonia), const.i.tuting more than nine tenths of their dry weight, may be evaporated by the a.s.sistance of decay or combustion. The organic part of _manures_ may be lost in the same manner; and, if the process of decomposition be continued long enough, nothing but a ma.s.s of mineral matter will remain, except perhaps a small quant.i.ty of carbon which has not been resolved into carbonic acid.

[What remains after manure has been long exposed to decomposition?

What gaseous compounds are formed by the decomposition of manures?]

The proportion of solid manure lost by evaporation (made by the a.s.sistance of decay), is a very large part of the whole. Manure cannot be kept a single day in its natural state without losing something. It commences to give out an offensive odor immediately, and this odor is occasioned, as was before stated, by the loss of some of its fertilizing parts.

Animal manure contains, as will be seen by reference to p. 100, all of the substances contained in plants, though not always in the correct relative proportions to each other. When decomposition commences, the carbon unites with the oxygen of the air, and pa.s.ses off as carbonic acid; the hydrogen and oxygen combine to form water (which evaporates), and the _nitrogen is mostly resolved into ammonia, which escapes into the atmosphere_.

[Describe fire-fanging.

What takes place when animal manure is exposed in an open barn-yard?

What does liquid manure lose by evaporation?]

If manure is thrown into heaps, it often ferments so rapidly as to produce sufficient heat to set fire to some parts of the manure, and cause it to be thrown off with greater rapidity. This may be observed in nearly all heaps of animal excrement. When they have lain for some time in mild weather, gray streaks of _ashes_ are often to be seen in the centre of the pile. The organic part of the manure having been _burned_ away, nothing but the ash remains,--this is called _fire-fanging_.