PRESENT PROBLEMS 337 



complicated proteids. There is no doubt that the protamines of one 

 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 proteo- 

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

 problem, 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 variations 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 character 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 solution of this problem promises much for the advance- 

 ment 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 pri- 

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

 have upon the general question of how far the lines of chemical decom- 

 position characteristic of each group of cells are dependent upon the 

 character of the anabolic processes by which that particular cell pro- 

 toplasm 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 fibres, 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 struc- 

 ture of the component 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 



