390 



SCIENCE 



[N. S. Vol. XXXVII. No. 950 



esses depends, then, upon accurate adjust- 

 ment and preservation of physico-chemical 

 conditions within the organism. Such con- 

 ditions as temperature, molecular concen- 

 tration and neutrality are now known to 

 be nicely adjusted and maintained; ad- 

 justed by processes going on in the body, 

 maintained by exchanges with the environ- 

 ment. This paper is concerned with those 

 physiological processes whereby the normal 

 reaction of the body fluids is permanently 

 preserved.^ 



Throughout the human body, while life 

 exists, there occurs a regular foi'mation of 

 acid substances, excretory products of 

 metabolism. As they form, these various 

 matters, carbonic acid, sulphuric acid and 

 phosphoric acid in the main, immediately 

 combine, but only partially, according to 

 their several avidities, with the basic con- 

 stituents of protoplasm and blood. In 

 pathological conditions great quantities of 

 aoetoacetic acid and /3-oxybutyric acid may 

 be produced and claim their share of base. 

 At irregular intervals varying quantities of 

 acids and bases pour in with the food. 

 Thus, through resulting changes in equi- 

 libria between bases and acids, normal 

 metabolism steadily operates to lower the 

 unvarying alkaline reaction (almost neu- 

 trality*) of the body. This tendency to 

 acidity is held sharply in check by special 

 protective mechanisms, acting coordinately, 

 in cooperation and regular succession. 



The chemical reactions whereby such 

 material is first neutralized, the chemical 

 substances which aid in neutralization, the 

 shares of more important substances in the 



' See L. J. Henderson, ' ' The Theory of Neu- 

 trality Regulation in the Animal Organism, ' ' 

 American Journal of Physiology, XXI., 427, 1908, 

 and "A Critical Study of the Process of Acid 

 Excretion," Journal of Biological Chemistry, IX., 

 403, 1911. 



* The terms may be used interchangeably for an 

 alkalinity which is so slight. 



process, and their efficiency, the changes in 

 chemical equilibria, including resulting 

 changes in hydrogen and hydroxyl ion con- 

 centrations, all, so far as they concern true 

 solution, are known with a fair approach 

 to certainty. Principally this work of 

 neutralization is done by salts of phosphoric 

 and carbonic acids, with aid from the 

 amphoteric proteins. In simplified form 

 the process may be represented by the two 

 reactions, 



M^HPO, -\-UA=MA + MH,PO,; 

 iWHCOa + 'E^ — MA-\- H,C03, 



where M stands for any basic radical, A 

 for any acid radical. Other less important 

 simultaneous reactions are of the same 

 type, except perhaps the union of the weak 

 acids with basic proteins like globine, and 

 the union of bases with more acid proteins. 

 Through the remarkable circumstance that 

 phosphates and carbonates possess, among 

 all Iniown chemical substances, the highest 

 power to preserve neutrality in solution,^ 

 this function is so well performed that the 

 alkaline reaction of the body scarcely 

 varies, even when the load upon the mech- 

 anism is heavy. 



But, however efficient such an arrange- 

 ment may be, it is of its very nature only 

 the first stage in the process of the excre- 

 tion of acid, and wholly dependent upon 

 constant support by the kidney, and of 

 course upon a supply of alkali in the food. 

 Regularly, as they form, the acid bodies 

 must be afforded alkali by blood and proto- 

 plasm, for every molecule of carbonic acid 

 about 0.93 molecule of alkali, for every 

 molecule of phosphoric acid 1.89 molecules 

 of alkali, and for every molecule of sul- 

 phuric acid 2 molecules of alkali, in accord- 

 ance with chemical laws and the normal 

 reaction of the body. Clearly, therefore, 



° L. J. Henderson, American Journal of Physi- 

 ology, XXI., 173, 1908. 



