THE INFLUENCE OF CHEMICAL FACTORS 75 



periments are rather large and the necessary corrections somewhat 

 uncertain. 1 Experiments on animals have given similar results. The 

 limit at which the oxygen absorption begins to fall lies somewhere 

 between 12 and 10 per cent, of oxygen in the inspired air (Friedlander 

 and Herter [1879], v - Terray [1896], Durig [1903]). 



All these results agree well with the blood gas determinations 

 made by Fraenkel and Geppert [1883] in experiments on dogs. They 

 found that the quantity of oxygen in the arterial blood did not become 

 appreciably diminished (thanks to the regulating mechanisms) before 

 the total pressure was lowered beyond 410 mm. (about 83 mm.) of 

 oxygen. At all higher pressures the average oxygen tension in the 

 capillaries must therefore remain practically constant, and there is no 

 reason why with a constant supply of oxygen the oxygen absorption 

 should not remain constant also. 



A diminution of the quantity of oxygen available in the arterial 

 blood will, according to the available experimental evidence, diminish 

 the oxygen absorption in warm-blooded animals, but experiments 

 cannot be carried far in this direction. When the oxygen supply is 

 deficient the qualitative character of the metabolism is changed. Acid 

 substances are liberated in the tissues and carbon dioxide washed 

 out. 



THE INFLUENCE OF HIGH OXYGEN PRESSURES ON THE RESPIRA- 

 TORY EXCHANGE OF WARM-BLOODED ANIMALS. 



The influence of high oxygen pressures on the respiratory exchange 

 of warm-blooded animals was investigated for the first time by 

 Lavoisier and Seguin [1814] who found that the respiratory exchange 

 is independent of the oxygen pressure. This result has been con- 

 firmed by all later observers, whether working on man or on animals 

 (Regnault and Reiset [1849], Lukjanow [1883], Fredericq [1884], de 

 Saint Martin [1884], Speck [1892], Loewy [1895], Durig [1903], 

 Schaternikoff [1904], Benedict and Higgins [1911]), and has been 

 called in doubt only by experimenters whose methods were manifestly 

 faulty (Rosenthal [1902]). Paul Bert [1878] found a maximum oxygen 

 absorption in air with about 50 per cent, of oxygen and a slight 



1 In experiments made at high altitudes in mountains (Schumburg and Zuntz [1896] ; 

 Zuntz, Loewy, Miiller and Caspari [1906] ; Jaquct and Stahelin [1900] ; v. Schrotter and 

 Zuntz [1902] and others) an increase in standard metabolism is regularly observed at 

 heights above 4000 m. and often also at lower heights, but in the opinion of the writer the 

 physiological conditions during mountain expeditions become too complicated to allow con- 

 clusions to be drawn with regard to the influence of the oxygen pressure taken by itself, 



