160 POPULAR SCIENCE MONTHLY. 



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 oxidation 

 and that which is derived from extra-cellular sources. A study of the 

 excretion of carbonic acid by fasting individuals, under different con- 

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

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

 ments 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 two-fold origin of this substance — endogenous and exogenous — 

 is most helpful in making clear many formerly obscure points connected 

 with the formation of this substance from the different classes of food- 

 stuffs. To-day, however, we understand quite clearly the genetic re- 

 lationship 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 eliminated 

 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 con- 

 tained 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 physiological 

 action as a fruitful subject for investigation. Many interesting facts 

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



