use of in tracking wounded animals or fugitives from justice.

"Soon the sagacious brute, his curling tail
Flourished in air, low bending, plies around
His busy nose, the steaming vapor snuffs
Inquisitive, nor leaves one turf untried,
Till, conscious of the recent stains, his heart
Beats quick; his snuffing nose, his active tail
Attest his joy: then with deep, opening mouth,
That makes the welkin tremble, he proclaims
Th' audacious felon : foot by foot he marks
His winding way, while all the listening crowd
Applaud his reasonings, o'er the watery ford,
Dry sandy heaths, and stony, barren hills;

O'er beaten paths, with men and beasts disdained,
Unerring he pursues, till at the cot

Arrived, and seizing by his guilty throat

The caitiff vile, redeems the captive prey.".

BOOK FOURTH.

I.

A

NIMALS eat that they may live. Man eats, not

only that he may live, but that he may gather strength, and fulfil his high destiny on earth.

When God gave form and animation to the dust of the earth, and man appeared, he did not intend that the sustenance of life should be left to chance or to careless selection. This intent of the Creator is revealed in the study of the organic world, where wonderful varieties and productions are offered to the appetite of man, in order that the "force of the universe may glow within his veins," and that the faculties of his mind may so expand that he may behold and comprehend the works and designs of his Maker.

Food, next to the purity of the air, determines the degree of the physical well-being; it gives the beauty of contour to the form; it builds up the marvellous structure of the brain; the ravishing smile of the features, the sublimity of thought, depend alike in great measure upon the benign influence of food.

It not only gives to nations their characteristics of strength and solidity, but it bestows upon society more of grace and refinement than philosophy is willing to allow.

II.

The question of alimentation with the civil laborer, exposed to healthy influences of properly distributed air and sunlight, and to the regular motions of a wellconducted life, is easy of solution to the inquiring mind.

But when it relates to the soldier, subjected to strange and unhealthy influences, the explanations involve much study, care, and research.

In the natural condition of man it is easy to determine how much food will support life and sustain physical exertion. The dietaries of the public institutions of different countries, the experiments of physiologists, and the records of history give the data with sufficient clearness. As to the amount of food required daily to repair the waste and wants of the human organism, much depends upon the degree of muscular exertion and nervous excitation, as well as the temperature of the season. In the alimentation of armies scientific principles must not be disregarded. Food must be considered as force; it must contain, not only material, but power. The strength of men, says Baron Liebig, is in direct ratio to the plastic matter in their food.

In determining the absolute quantities of nutrient substances required by the system, Lehman observes that there are three magnitudes especially to be considered.

The first is the quantity requisite to prevent the animal from sinking by starvation. The second is that which affords the right supply of nourishment for the perfect accomplishment of the functions, and the last is that which indicates the amount of nutrient matter which

may, under the most favorable circumstances, be subjected to metamorphosis in the blood. No one of the four classes, the carbohydrates, the fats, the albuminous matters, and the salts, will answer the purpose alone, but all must be employed together, and this invariable proportion according to the local, and, therefore, variable waste of the system. These considerations indicate how complicated the problem is.

III.

Life is an action; the principle of life, whatever may be its nature, is eminently and visibly a principle of excitation, of impulsion, a motive power.

"It is taking a false idea of life," says Cuvier, "to consider it as a simple link which binds the elements of the living body together, since, on the contrary, it is a power which moves and sustains them unceasingly."

These elements do not for an instant preserve the same relation and connection; or, in other words, the living body does not for an instant keep the same state and composition. "This law," adds Flourens, "does not affect alone the muscles, viscera, and tissues, but there is a continual mutation of all the parts composing the bone." These views have been substantiated by the extended experiments of Chossat, of Von Bibra, and a host of experimentalists, showing how positive and decided are the changes in the material composition of the body, and especially the constitution of even the bone from the influence of food.

IV.

"It is from the blood that life derives the principles which maintain and repair it. The more vigorous, plastic, and rich in nutritive material, so much the more life increases and manifests itself, so much the quicker the reparatory processes restore a lesion to its natural condition.

"The blood owes its vivifying properties to the presence of oxygen, which it receives by the respiratory organs; but that nourishing fluid, to complete its physiological rôle, needs to receive combustible and organizable material."

These Protean principles of the healthy blood form one fifth of its weight.

Oxygen unites with the carbon of the food in the blood of animals; carbonic acid is formed and heat evolved. When the atmosphere is vitiated, the oxygenating processes are diminished in ratio to the vitiation.

The experiments of Seguin, Crawford, and De la Roche show that in a vitiated and highly heated atmosphere the blood is not thoroughly decarbonized, thereby deranging the nervous system, and affecting the animal functions as well as the mental faculties. The blood is subject to incessant variations. The more feeble the respiration the less rich it is. Man absorbs twenty to thirty quarts of oxygen every hour. The pure air is a real food, and is as necessary for the development and repair of the physical force as the more solid forms of matter. Nine ounces of carbon are consumed every day, and the phenomenon. of the expired carbonic acid has its maxima and minima