1 52 POPULAR SCIENCE MONTHLY. 



type or another are integral parts of every proteid molecule, and when 

 their chemical constitution is made quite clear, much will have been 

 accomplished toward a fuller understanding of the more complicated 

 forms. 



It needs no imagination to foresee what a full knowledge of the 

 chemical constitution of all types of proteid matter will mean for the 

 physiologist and physiological chemist. Much that is now cloudy and 

 uncertain in our understanding of cell and tissue metabolism, in our 

 comprehension of nutritive changes in general, of digestive proteolysis 

 and of intracellular autolysis, will become clear as crystal. The prob- 

 lem, however, is not a simple one, but is exceedingly complex, for it is 

 to be remembered that just as the individual proteids differ from each 

 other in superficial reactions and characteristics, so do they undoubtedly 

 differ in their inner structure. Hence, we must expect to find varia- 

 tions in the make-up of the individual molecules, and it is one of the 

 most important problems of to-day to ascertain the nature of these 

 chemical variations, to recognize the individual groups that give charac- 

 ter to the molecules and to learn how these groups are bound together 

 to make the typical proteid of this and that tissue or organ. The solu- 

 tion of this problem promises much for the advancement of physiological 

 chemistry, but it holds out the promise of even more for the good of 

 physiology in general, since there is bound up in the chemical structure 

 of the proteid molecules a full and complete explanation of tissue 

 changes, and of many metabolic phenomena which to-day are as sealed 

 volumes. 



The development of our knowledge regarding the cell as a physio- 

 logical unit has led to a fuller recognition of the importance of dis- 

 criminating between the primary and secondary cell constituents. As 

 a result, the physiological chemist has come to realize the necessity of 

 more exact knowledge as to the nature and distribution of the primary 

 components of cells, because of the bearing this knowledge may have 

 upon the general question of how far the lines of chemical decomposi- 

 tion characteristic of each group of cells are dependent upon the charac- 

 ter of the anabolic processes by which that particular cell protoplasm 

 is formed, and how far the peculiar katabolic or retrogressive changes 

 of that group of cells are due to outside influences, exerted by specific 

 nerve fibers, or by the character of the blood and lymph stream. The 

 physiological chemist would know whether the secret of glandular 

 secretion, of tissue changes, of metabolic activity, is to be found in the 

 particular forms of protoplasm that enter into the structure of the com- 

 ponent cells, whether it is associated in any way with some inherent 

 quality of the primary cell constituents. 



There is something marvelous in the unerring certainty with which 

 a given group of cells performs its work, never deviating a hair's breadth 



