THE RELATION OF THE HEART-BEAT TO ELECTROLYTES. 177 



it is alkaline. For instance, the P + of centi-normal hydrochloric acid 



H 

 is 2, that of milli-normal sodium hydroxide 11, and so forth. Now 

 the solution of pure salts of strong acids and strong bases in distilled 

 water, neutral by intention, becomes in the course of preparation very 

 faintly acid as it reaches equilibrium with the small concentration of 

 COo present in the air. The reaction of pure water or of a solution of 

 salts of the type we have just mentioned, which do not themselves affect 

 the reaction, is very easily shifted by minute additions of acid or alkali. 

 Thus one drop ("05 c.c.) of normal hydrochloric acid would suffice to 

 change the P -t- of fifty litres of water irom 7 to 6. But if the origin- 



H 

 ally neutral solution contained a weak acid balanced against a salt 

 of the same weak acid with a strong base, the addition of the same 

 amount of acid as before would not appreciably disturb the P + . Such 



H 

 a condition is realized, for example, in a saline solution containing a 

 little sodium bicarbonate and carbonic acid. Such a solution may be 

 prepared with the same P + as the purest water : it will differ from 



H 

 water in that its P + is much more stable — that is to say, it is displaced 



H 

 very much less by the addition of the same small traces of acid or of 

 alkali. Substances having this effect on addition to a solution are spoken 

 of by Sorensen as " buffers." Amphoteric electrolytes such as the 

 amino-acids and their compounds the proteins tend also to stabilize the 

 reaction of solutions in which they are present. The explanation of 

 the action of all these substances lies in the fact that when they are 

 present in a solution the hydrogen ion concentration is u function of 

 more than one equilibrium. It should be noted in passing that in 

 nature such "buffers" play an important role. For instance, the 

 carbonates, phosphates, and proteins in the blood serve to limit the 

 changes in P+ of that fluid resulting from the production of acid 



H 

 metabolites by the tissues, the secretion of acid or of alkaline fluids, 

 and tlie removal of carbonic acid in the lungs, to such values that the 

 limits of safety are never passed. If the blood could be deprived of 

 these substances, it is probable that the acid produced in moderate 

 exercise for example would so raise the H" concentration as completely 

 to disorganize nerve cells and heart, instead of altering it only to such 

 an extent as to cause the blood to act as a chemical messenger or 

 hormone, modifying the activities of nerve cells and heart in such a 



