A text-book of physiological chemistry for students of medicine and physicians / By Charles E. Simon.

  • Simon, Charles E. (Charles Edmund), 1866-1927.
Date:
1907
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of physiological chemistry for students of medicine and physicians / By Charles E. Simon. 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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    Character of Chemical Changes.—The chemical processes which are involved in the transformation of non-living matter into living tissue are qualitatively the same in plants and animals. Quantitative differences, however, exist, which are sufficiently pro- nounced to serve as marks of distinction between animals and plants. Thus plants are capable of evolving from relatively simple compounds those complex chemical substances which go to form their structure, while animals apparently do not possess this power. They are hence dependent for their existence upon food-stuffs which are preformed; and the potential energy which animals require for the functioning of their various organs, and which they trans- form into kinetic energy, is, as a matter of fact, derived in every instance, either directly or indirectly, from plant-life. Plants, in turn, obtain the potential energy which is stored in their tissues from the kinetic energy of sunlight, and in virtue of this energy can elaborate those simple chemical substances which are at their dis- posal as food-stuffs into the complex bodies which constitute their tissues. We thus observe that while in plant-life synthetic chemical processes prevail, analytical processes are foremost in animal life. These analytical processes, moreover, are largely of the character of oxidations, while the syntheses which are effected in the bodies (if plants are essentially of the nature of reductions. But just as syn- thetic processes are not absolutely characteristic of plant-life, so also do oxidation-processes occur in plants, and synthetic reductions in animals. This becomes especially noticeable as we descend in the scale of both animal and vegetable life. Primitive vegetable organisms are thus met with which, like the highly organized mam- mal, are almost entirely dependent for their existence upon already elaborated food-stuffs, and low forms of animal life similarly occur in which the processes of nutrition are essentially the same as those which occur in the higher plants. The differences which thus exist between animal life and plant-life are therefore, as has been stated, more of a quantitative than a qualitative kind. Synthetic Processes in Plants.—I have said that plants are capable of elaborating from simpler compounds the complex chem- ical substances of which they are composed, and that the chemical processes here involved are essentially of the nature of synthetic reductions. Formerly, it was believed that the various organic sub- ■stances which occur in animals and plants could be produced only through the agency of a special vital force; but we now know that this is not necessarily the case, and that as a matter of fact a large number of such bodies can be produced artificially in the chemical laboratory. Wohler, in 1829, was the first to demonstrate this possibility by preparing urea from ammonium cyanate. This he accomplished by heating the substance to a temperature of 100° C, when a transposition of atoms apparently takes place, and urea results. The force which is necessary to effect such a change is