Hand-book of physiology / by W.M. Baker and V.D. Harris.

  • Kirkes, William Senhouse, 1823-1864.
Date:
1884
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of physiology / by W.M. Baker and V.D. Harris. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    alteration in the chemical constitution of the material which is taken up and added to the previously existing mass. For example, when a crystal of common salt grows on being placed in a fluid which contains the same material, the properties of the salt are not changed by being taken out of the liquid by the crystal and added to its surface in a solid form. But the case is essentially different in living beings, both animal and vegetable. A plant, like a crystal, can only grow when fresh material is presented to it; and this is absorbed by its leaves and roots; and animals, for the same purpose of getting new matter for growth and nutrition, take food into their stomachs. But in both these cases the materials are much altered before they are finally assimilated by the structures they are destined to nourish. (4.) The growth of all living things has a definite limit, and the law which governs this limitation of increase in size is so invariable that we should be as much astonished to find an individual plant or animal without limit as to growth as without limit to life. Development is as constant an accompaniment of life as growth. The term is used to indicate that change to which, before maturity, all living parts are constantly subject, and by which they are made more and more capable of performing their several functions. For example, a full-grown man is not merely a magnified child ; his tissues and organs have not only grown, or increased in size, they have also developed, or become better in quality. No very accurate limit can be drawn between the end of de- velopment and the beginning of decline; and the two processes may be often seen together in the same individual. But after a time all parts alike share in the tendency to degeneration, and this is at length succeeded by death. Differences between Plants and Animals.—It has been already said that the essential features of life are the same in all living things ; in other words, in the members of both the animal and vegetable kingdoms. It may be well to notice briefly the distinctions which exist between the members of these two king- doms. It may seem, indeed, a strange notion that it is possible to confound vegetables with animals, but it is true with respect to the lowest of them, in which but little is manifested beyond the essentials of life, which are the same in both. b 2