246 SCIENCE PROGRESS. 



body we know that the absence of as little as sVth of the 

 quantity of oxygen present in blood saturated with air 

 would reduce the oxygen tension in the blood from 20 '9 per 

 cent, to half this value. 



A further probable source of fallacy in the aerotono- 

 meter method lies in the fact that as proved by Pfliiger a 

 very appreciable amount of oxidation occurs spontaneously 

 in arterial blood within an exceedingly short interval of 

 time after it has left the lungs. The rapid darkening of 

 the blood in consequence of this change can easily be seen 

 in arterial blood collected over mercury, and has also been 

 observed by Pfliiger to occur in the blood within the crural 

 artery if the latter be excluded for a few seconds. The 

 occurrence of oxidation, to even a fraction of the ex- 

 tent observed by Pfliiger, in the blood on its way from 

 the lung to the aerotonometer would cause most serious 

 fallacy. 



The subject of the causes of interchange of oxygen 

 between the blood and alveolar air was again taken up by 

 Dr. Lorrain Smith and myself about two years ago. 1 The 

 method we employed is a new one, and depends on the 

 well-known fact that haemoglobin combines with either 

 oxygen or carbonic oxide, the carbonic-oxide compound 

 being, however, much the more stable one. When haemo- 

 globin solution or undiluted blood is brought into contact 

 with a gas mixture containing both oxygen and carbonic 

 oxide, the haemoglobin combines partly with the oxygen 

 and partly with the carbonic oxide, the final result being 

 dependent, according to a definite and sharply defined law, 

 on the relative tensions of the two gases. Thus if the 

 gas mixture contain 20 '9 per cent, of oxygen and '070 per 

 cent, of carbonic oxide, the haemoglobin shares itself equally 

 between the two gases. The partition is the same whether, 

 within certain limits, the atmospheric pressure or the tem- 

 perature is raised or lowered, or whether by the addition 

 or subtraction of nitrogen the percentages of oxygen and 

 carbonic oxide are increased or diminished in corresponding 



1 Journal of Physiology, vol. xviii., pp. 201 and 430; vol. xx., p. 497 ; 

 vol. xxii., pp. 231, 307. 



