An American text-book of physiology / by Henry P. Bowditch [and others]., edited by William H. Howell.

  • William Henry Howell
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: An American text-book of physiology / by Henry P. Bowditch [and others]., edited by William H. Howell. 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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    a much greater power of assimilalioii. Owing to tlii.s latter property tlie plant-cell is able, 'vvitii the aid ol solar energy, to construct its protoplasm from very simple forms of inorganic matter, such as water, cari)on dioxide, and inorganic salts. In this way energy is stored within the vegetable cell in the form of complex organic compounds. Animal ])rotoplasm, on the con- trary, has comparatively feeble synthetic properties ; it is characterized chiefly by its destructive jiower. In the long run, animals obtain their food from the plant kingdom, and the animal cell is able to dissociate or oxidize the com])lex material of vegetable protoplasm and thus liberate the potential energy con- tained therein, the energy taking the form mainly of heat and muscular work. We must suppose that there is a general resemblance in the ultimate structure of animal and vegetable living matter to wdiich the fundamental similarity in properties is due, but at the same time there must be also some common dif- ference in internal structure between the two, and it is fair to assume that the divergent properties exhibited by the two great groups of living things are a direct outcome of this structural dissimilarity; to make use of a figure of speech employed by Bichat, plants and animals are cast in different moulds. It is difficult if not impossible to settle upon any one property which absolutely shall distinguish living from dead matter. Xutrition, that is, the power of converting dead food material into living substance, and repro- duction, that is, the power of each organism to perpetuate its kind by the formation of new individuals, are probably the most fundamental charac- teristics of living things; but in some of the specialized tissues of higher • animals the power of reproduction, so far as this means mere multiplication by cell-division, seems to be lost, as, for example, in the case of the nerve-cells in the central nervous system or of the ovum itself before it is fertilized i)y the spermatozoon. Nevertheless these cellular units are indisputably living matter, and continue to exhibit the power of nutrition as well as other prop- erties characteristic of the living state. It is possible also that the jxtwer of nutrition may, under certain conditions, be held in abeyance temporarily at least, although it is certain that a permanent loss of this property is incom- patible with the retention of the living condition. It is frequently said that the most general property of living matter is its irritability. The precise meaning of the term vital irritability is hard to define. The \yord implies the capability of reacting to a stimulus and usually also the assumption that in the reaction some of the inner potential energy of the living material is liberated, so that the energy of the res]M)nse is many times greater, it may be, than the energy of the stimulus. This last idea is illustrated by the case of a contracting muscle, in Ayhich the stimulus acts as a liberating force causing chemical decompositions of the substance of the muscle with the liberation of a comparatively large amount of energy, chiefly in the form of heat or of heat and work. It may be remarked in ])assing, liowever, that we are not justified at present in assuming that a similar liberation of stored energy takes place in all irritable tissues. In the case of nerve-fibres, for instance, we have a typically irritable tissue which responds readily to
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