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ing and of elaborating food into chyle, and the organic and vital power of extracting the elements of repair from the blood, diminish in activity. Thence, although the aged often take as much food as the adult, they become thin, and waste in volume. In those in whom the tendency to the deposit of fat persists in old age, the waste of the organs is concealed by the layers of adipose substance which are formed underneath the skin, and which surround all the organs; but the shrinking and wasting of the muscles and of the other organs is not the less real, as I have often found in making post-mortem examinations of very fat elderly people.

As a necessary result of diminished digestive vitality, organic combustion languishes. Hence the chilliness of the aged, increased by the greater slowness of their circulation. The blood, circulating less rapidly through the lungs and the body generally, is less charged with oxygen; and the elements of combustion being less abundant, organic combustion takes place less rapidly, and less heat is generated. Thus is explained the cold hands and feet of the aged, and the necessity for artificial heat and warm clothing. Thence it is that the old man seeks the sun, and that we find him in the country sitting at his door for hours basking in the sun, seeking from its genial rays the warmth which the organic processes no longer afford, as in former days the days of his youth and of his organic vigour.

As the current of human existence runs on, all these evidences of deficient nutritive power increase, and to them is often added the fatty degeneration of important organs; by which, if extreme, the thread of life may be brought to a close. The muscular powerlessness of old age is owing partly to diminished volume of the muscles, partly to the replacement of non-repaired muscular fibre by fat, and partly to weakened circulation and innervation. The loss of nervous power, and the weakening of the memory and of the intellect of the aged, is often attributable to fatty transformation. The wear and tear of the nervous substance of the brain is not effectually repaired, fat takes its place, and the powers of the nervous centre are for ever obscured.

At last nutrition ceases, and death ensues. The vital spark no longer vivifies the human clay, and its complex machinery is hushed for ever. Organic repair has been brought abruptly to a close, the human fire is quenched, and heat no longer being generated, the body rapidly loses its caloric to the surrounding atmosphere; until, after a few hours, the marble cold of death has seized upon the tenement so long the abode of the organic processes we have described.

With those, however, who leave progeny, nutritive death can hardly be said to take place; their vitality survives in their children. The vital nutritive force which gradually built up the parent

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organization, repaired its waste, and enabled it to resist the destructive influences by which it was surrounded, is transferred in all its pristine vigour and freshness to its offspring. The latter grow and flourish, as the parents decay and perish.

As with the animal, so with the vegetable world; all organized creations contain the seeds of death from the first. In all, the nutritive force for a time is vigorous and energetic; powerful to produce and keep up the organized structure. In all, after a certain lapse of time, when reproduction has been accomplished, the vital power becomes less and less energetic. Finally, when decay has stamped its impress on the organization, has destroyed both beauty and usefulness, the nutritive force expires, and death ensues. Thus space is made on the earth for the young, who unite the attributes which their parents have lost-beauty and power. Thus it is that the earth remains ever young and ever fair;-youthful and vigorous organizations ever replacing those which have fallen into decay and perished, through the weakening and final arrest of the original nutritive force.

CHAPTER IV.

NUTRITION IN ANIMALS.

NUTRITION in animals follows precisely the same law as in man, with slight differences, deduced principally from the fact that man is omnivorous, whereas by far the larger proportion of animals are either frugivorous, herbivorous, or carnivorous. That man is destined to live on a mixed dietary, partly animal, partly vegetable, is shown by his teeth, as we have seen, p. 68. Some resemble the teeth of the rodent or frugivorous animals, some those of the herbivorous, and some those of the carnivorous. It is also shown by his intestinal canal, which occupies a medium position, being neither as long nor as complex as that of herbivorous animals, nor as short as that of the

carnivorous.

Frugivorous and herbivorous animals find in the grains and in the grasses which they consume the chemical elements of nutrition, required for the nutritive growth and repair of their organization-viz., carbon, nitrogen, and hydrogen, oxygen

and salts; the oxygen, as with man, being principally furnished by the atmosphere during respiration. Nitrogen is present in grain and in grasses, and from it are the albumen and fibrin of the organic tissues generated. The carbon and hydrogen, which form the principal bulk of the vegetable food of the herbivora, are, on the one hand, converted into fat by the nutritive process, and on the other, are burnt in creating animal heat and force, as in man.

From these facts we might conclude that, for herbivorous animals to thrive and do well, a large amount of vegetable food must be consumed. And such is really the case, herbivorous animals requiring a large bulk and weight of the substances on which they live, in order that they may find in it enough nitrogen to form their often huge frames, and enough carbon and hydrogen to produce, by its combustion, the heat they require to make good the constant loss from exposure to atmospheric influences. The generation of heat and force, from organic combustion, must, indeed, be very great, when we consider how well they bear exposure to cold, night and day, in all climates, often during very rigorous weather, and the amount of force they expend.

Carnivorous animals find the elements of nutrition already elaborated and prepared for them in the flesh and fat of their victims. Consequently a less complex and shorter intestinal tube answers all the

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