PRESENT PROBLEMS 345 



Equally important is it for the physiologist to know more fully 

 regarding the sources of the carbonic acid resulting from oxidation in 

 the body. What proportion of the ever-varying output of this gaseous 

 product of metabolism comes from the oxidation of organized tissue- 

 material, and what from the oxidation of circulating carbohydrate and 

 fat and unorganized material in general? We have learned, for ex- 

 ample, that the excretion of carbonic acid runs more or less closely 

 parallel with the degree of muscular activity, and we should possess the 

 means of discriminating between the output from true tissue-oxida- 

 tion and that which is derived from extracellular sources. A study of 

 the excretion of carbonic acid by fasting individuals, under different 

 conditions of life and activity, would be helpful in throwing light upon 

 this question, and also in giving us a clearer idea of the minimal re- 

 quirements of the body for non-nitrogenous foods to make good the 

 loss of energy in heat-liberation, muscular work, etc. By such a study 

 we might hope for added light upon that much-discussed problem, the 

 source of the energy of muscular contraction. While most physiologists 

 are certainly agreed that this energy comes preferably from the oxida- 

 tion of non-nitrogenous matter, there remain many obscure points 

 upon which we need enlightenment. 



We likewise need fuller and more exact knowledge of the ways in 

 which uric acid originates in the body, especially regarding its rela- 

 tionship to intracellular decomposition. Our present understanding 

 of the twofold origin of this substance endogenous and exogenous 

 is most helpful in making clear many formerly obscure points con- 

 nected with the formation of this substance from the different classes 

 of food-stuffs. To-day, however, we understand quite clearly the gene- 

 tic relationship between the free and combined purin bases and uric 

 acid, but we are still uncertain whether this substance is formed to 

 some extent synthetically and whether when once formed it is all elim- 

 inated unchanged or undergoes oxidation, in part, into less harmful 

 substances. In other words, we do not yet know how far the uric acid 

 which is contained in the daily urine is a measure of the production of 

 uric acid for the twenty-four hours. Uric acid and the alloxuric bases 

 are such important substances, in their influence upon health and the 

 general nutritive condition of the body, that it is extremely important 

 for us to know more concerning their origin and their ultimate fate 

 in the body. We may likewise inquire where uric acid is formed. Does 

 it originate entirely in the liver, or are there other depots where it is 

 produced and collected? 



Turning our attention now in another direction, we may revert to 

 the relationship between stereochemical configuration and physiolog- 

 ical action as a fruitful subject for investigation. Many interesting 

 facts have already been gleaned, and certain general rules or laws 

 have been formulated, connecting given lines of physiological action 



