212 ELECTROCHEMISTRY 



concentration in normal blood at physiological CO2 pressures 

 (0.028 to 0.054 atmosphere) being, according to recent deter- 

 minations, about 0.37 X 10~'. 



Friedenthal (19) and von Szily (69), employing a somewhat 

 different method of investigation, have reached the same con- 

 clusion as the above quoted observers. They utilized the indi- 

 cator-method of Friedenthal, Fels and Salm. Mixtures of acid 

 and basic phosphates of known H+ and OH' content (determined 

 by Salm, using the potentiometric method) were tinged with a 

 number of different indicators and the samples of the body- 

 fluid under examination were tinged with equal quantities of 

 the same indicators — the colors of the two series of fluids were 

 then compared. The phosphate-mixture which approximated 

 most closely in its indicator reactions to the normal blood-serum 

 had an acidity corresponding to 6.5 X 10~^ H+, absolute neutrality 

 being 8 X lO-^ H+. 



Moreover the investigations of Friedenthal (19) (20) and of 

 Foa (15) (16) (17) have shown that not only is the blood almost 

 exactly neutral but that almost all of the tissue-fluids are also 

 approximately neutral. Thus, the pancreatic juice of a dog, one 

 of the most alkaline of the body-fluids, contained 5 X 10~^ H+, 

 corresponding to an alkalinity of 13 X 10"'^ OH'. Hitherto, ac- 

 cording to Friedenthal (20), no animal fluid has been found con- 

 taining less than 10~^°i\r H+, that is, more than about 6 X 10~^ 

 N OH'. The gastric juice of a dog was, however, found to be 

 1000 times more acid than the pancreatic juice is alkaline, that 

 is, it possessed the acidity of, approximately, a hundredth normal 

 solution of HCl. 



With few exceptions, therefore, the tissue fluids are practically 

 neutral in reaction. It is a significant fact also (Friedenthal 

 (20), Loeb (37)) that the naturally occurring waters, in which 

 the lives of aquatic animals are spent, are also very nearly neutral 

 in reaction. "We may therefore draw the conclusion that life- 

 phenomena occur in a neutral liquid" (Loeb, loc. cit.), and, more- 

 over, save in certain special localities, such as the internal wall 

 of the stomach, the life-process occurs exclusively in a neutral 

 milieu; thus even an increase of 50 per cent in the minute H+ 

 concentration of normal blood induces profound toxic symptoms, 

 and an increase to 1 X 10~^ N H+ induces fatal acidosis. 



In view of the fact that the products of metabolism include a 



