Page:Popular Science Monthly Volume 66.djvu/165

Rh formulated, connecting given lines of physiological action with a definite chemical structure. Thus, it is well understood to-day, for example, that all substances which contain a nitro or nitroso group united with, or bound to, oxygen have the effect of dilating blood vessels, while, on the other hand, substances which contain the same nitro or nitroso group joined to carbon have a quite different physiological action, being mostly blood poisons. Further, nitrils, R. CN, tend to produce coma, while isonitriles, R., are much more toxic and tend to produce paralysis of the respiratory center. In other words, it is clearly manifest that certain definite groupings within the molecule are the cause of the physiological action of the molecule. At the same time, it is also known that in order to have the physiological action of a substance manifest not only must it contain the necessary group or groupings, but there must likewise be present a second group which has the power of combining with and holding fast to the tissue upon which the physiological action manifests itself. Slight chemical alteration of a substance may, therefore, interfere with or nullify its ordinary physiological action without necessarily altering the physiologically active groups; but by simply changing these other groups through which the molecule ordinarily attaches itself, so that the latter can no longer adhere to the cell substance or tissue protoplasm, there occurs a consequent loss of physiological action.

Another fact clearly understood is that two substances having the same nucleus and like side chains, with an entirely similar grouping, may still be physiologically unlike, owing to a different arrangement in space. This is well illustrated by the dextro- and lævo-rotary tartaric acids, one of which is readily utilized by Penicillium glaucum as nutriment, while the other can not be so consumed. Many other illustrations might be cited, especially with various types of organic poisons, all tending to show that physiological action is dependent upon the arrangement of the atoms or radicles in space, as well as upon the nature of the atoms or radicles. With these facts before us, we see many lines of inquiry presenting themselves, many problems demanding solution, with reference both to pharmacology and physiology.

Confining our attention more especially to physiological matters, we are certainly justified in considering the application of these principles to many of the substances conspicuous in the processes of the body. The work and suggestions of Pasteur and Emil Fischer have indicated certain possibilities regarding the nature and action of enzymes, not to be overlooked. Stereochemical configuration may be just as much responsible for enzyme action, for proteolysis, amylolysis, etc., as any other feature of the active molecule, and how far other lines of physio