346 PHYSIOLOGICAL CHEMISTRY 



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 isonitrils, R. N = C, are much 

 more toxic and tend to produce paralysis of the respiratory centre. 1 

 In other words, it is clearly manifest that certain definite group- 

 ings 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, there- 

 fore, 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 group- 

 ing, may still be physiologically unlike, owing to a different arrange- 

 ment in space. This is well illustrated by the dextro- and Isevo-rotary 

 tartaric acids, one of which is readily utilized by Penicillium glaucum 

 as nutriment, while the other cannot 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 physio- 

 logy. 



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- 

 logical action may be due to chemical structure and the configuration 

 1 See Frankel Ergebnisse der Physiologie, Dritter Jahrgang. Biochemie, p. 291. 



