Principles of human physiology / by William B. Carpenter ; edited by Henry Power.

  • William Benjamin Carpenter
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: Principles of human physiology / by William B. Carpenter ; edited by Henry Power. Source: Wellcome Collection.

    41/1242 (page 7)
    to place its dependence on that agency beyond reasonable question; so that we seem fully entitled to say that Heat, acting through the germ, becomes the constructive force or power by which the Vegetable fabric is built up.* But there appears to be anotlier source of that power in the Seed itself. In the conversion of the insoluble starch of the Seed into sugar, and probably also in a further metamorphosis of a part of that sugar, a large quantity of carbon is eliminated, by combining with the oxygen of the air so as to form carbonic acid; this combination is necessarily attended with a disengagement of heat, which becomes very sensible when (as in malting) a large number of germinating seeds are aggregated together; and it cannot but be regarded as probable that the heat thus evolved within the seed concurs with that derived from without, in supplying to the germ the force that promotes its evolution. 9. The condition of the Plant which has attained a more advanced stage of its development, differs from that of the germinating embryo essentially in this particular, that the organic compounds which it requires as the materials of the extension of the fabric are formed by itself instead of being supplied to it from without. The tissues of the green surfaces of the leaves and stems, when acted on by light, have the peculiar power of generating at the expense of carbonic acid, water, and ammonia, various ternary and quarternary Organic compounds, such as chlorophyll, starch, oil, and albumen; and of the compounds thus generated, a part are ap - propriated by the constructive force of the Plant (derived from the heat with which it is supplied) to the formation of new tissues; whilst a part are stored up in the cavities of those tissues, where they ultimately serve either for the evolution of parts subsequently developed, or for the nutrition of Animals which employ them as food. Of the source of those peculiar affinities by which the components of the Starch, Albumen, &c. are brought together, we have no right to speak confidently; but looking to the fact that these compounds are not produced in any case by the direct union of their elements, and that a decomposition of binary compounds seems to be a necessary antecedent of their formation, it is scarcely improbable that, as suggested by Prof. Le Conte,] that source is to be found in the chemical forces set free in the preliminary act of decomposition, in which the elements would be liberated in that 'nascent condition' which is well known to be one of peculiar energy. The in- fluence of Light, then, upon the Vegetable organism appears to be essentially exerted in bringing about what may be considered a higher mode of chemical combination between oxygen, hydrogen, and carbon, with the addition of nitrogen in certain cases ; and there is no evidence that it extends beyond this. That the appropriation of the materials * The effect of Heat is doubtless manifested very differently by different seeds; such variations being partly specific, partly individual. But these are no greater than we see in the Inorganic world; the increment of temperature and the augmentation of bulk exhibited by different substances when subjected to the same absolute measure of heat, being as diverse as the substances themselves.—The whole process of'malting,' it may be remarked, is based on the average regularity with which the seeds of a par- ticular species may be at any time forced to a definite rate of germination by a definite increment of temperature. f See his very suggestive Memoir ' On the Correlation of Physical, Chemical, and Vital Force,' in the Philosophical Magazine for J 860, vol. xix. Ser. iv. p. 137.