OF VITAL PHENOMENA 183 



tension of the alveolar air. Since more exact data on the alveolar 

 air are available we may take them as the most reliable index 

 of the changes in the buffer value of the blood. Barcroft (1914) 

 measured the C0 2 tension of the alveolar air, but put most reli- 

 ance on the H ion concentration of the blood at a certain C0 2 

 tension. In this way the buffer value is indicated as shown in 

 Fig. 18. Barcroft estimated the H ion concentration of the blood 

 by its effect on the dissociation of oxyhemoglobin. 



Hasselbalch and Gammeltoft (1915) observed a lowering of 

 the C0 2 tension on a meat diet. This suggests an explanation 

 of the so-called dynamic action of protein (Lusk, 1915). On 

 . passing from a protein poor to a protein rich diet the heat output 

 of the body is increased, even though the available energy of the 

 food is not. Since the C0 2 tension of the alveolar air is de- 

 creased, the lung ventilation must be increased and the oxygen 

 carried to the tissues increased as well. Perhaps the greater heat 

 production is the direct result of this increased oxygen supply. 

 If this be true, we may suppose that the amino acids arising from 

 digestion of the protein increase the H ion concentration of the 

 blood, and stimulate the respiratory center, increasing lung ven- 

 tilation, this in turn increasing oxidation. Since the respiratory 

 center is more sensitive to changes in H ion concentration than 

 any apparatus available for measuring it, a failure to determine 

 any increase in the H ion concentration of the blood is to be 

 expected. It was shown by Haldane and Priestley (1905) that 

 a 0.2 per cent rise in the C0 2 tension of the alveolar air doubles 

 lung ventilation. A reference to Fig. 18 shows that this causes 

 only a minute change in the PH (a change too small to measure 

 with certainty on a carbonated fluid like the blood). 



We may conclude from the foregoing that the buffer value of 

 the blood is lowered by a meat diet. The same seems to be pro- 

 duced during exercise, acclimatization to high altitudes, preg- 

 nancy, diabetic coma and other conditions of acidosis. On the 

 contrary, the experiments of Van Slyke, Cullen and Stillman 

 (1915) indicate that the buffer value of the blood is increased 

 during protein digestion. This may be due to the passage of CI 

 ion9 from the blood to the stomach with consequent increase in 

 the bicarbonate content of the blood. 



It seems probable that the P'H of the blood of all animals is 



