Page:Popular Science Monthly Volume 21.djvu/374

362 structure and perturbations of function to which living matter is liable; and, secondarily, medicine deals with the applications of the knowledge thus acquired for the checking of these perturbations and the renewal of normal structures—in other words, for the relief of suffering and the restoration and preservation of health.

The Held of medicine is, then, a large one. As already intimated, some knowledge of the various natural sciences is essential to its successful study; not only by reason of the fact that living matter is subject to the same chemical and physical laws as non-living matter, but also because of the intimacy of its relations to its physical environment, and of the constancy of the reactions between every organism and its environment.

As a general introduction to the course of medical study now opened in this college, it has therefore seemed appropriate to devote an hour to a brief biography of Protoplasm, the universal life-substance from which all organisms, whether vegetable or animal, originate, and modifications of which constitute even the most complex tissues of the highest animal forms.

Though so universally diffused, though the autobiography of protoplasm has been written in the life of every plant and animal since creation's dawn, it is still a hidden story in some of its earlier chapters. Perhaps it is the very simplicity of its origin that balks us: we would fain invoke some supernatural explanation of the growth-force and the capacity for development which belong to this substance, as distinct from non-living matter, forgetting that all natural forces are equally elusive and obscure. Why do certain kinds of matter always crystallize in certain fixed and characteristic forms? Why, on the other hand, is protoplasm formless, but capable of endless development and change?

There are certain chemical and physical differences between crystallizable and non-crystallizable substances which, if fully understood, would no doubt furnish an answer to this question.

Protoplasm, a non-crystallizable substance, is both physically and chemically of a highly complex composition not determined with exactness, but known to consist mainly of hydrogen, oxygen, nitrogen, and carbon, variously combined in such proportions as to produce representatives of three classes of chemical substances—the albuminoids, the starches, and the fats—the albuminous constituents largely predominating in native undifferentiated protoplasm.

With these compounds is associated a considerable though varying proportion of water, as well as smaller quantities of saline and other crystalline substances.

Of the molecular structure of living, active protoplasm, nothing definite is known; it is, however, probable that the albuminoid matter of its massive molecule is associated with a complex fat and with some form of starch; while the water and the salts may be loosely combined