RESPIRATION 



157 



The reason why anoxaemia is absent in persons who are in 

 good training will be discussed in Chapter IX. 



There can be little doubt, in view of all the evidence adduced 

 above, that muscular work produces some degree of anoxaemia 

 in untrained persons, and that the anoxaemia increases with the 

 work. The anoxaemia can hardly be due to any other cause than 



that the blood is passing through the lungs so quickly that suffi- 

 cient oxygen to saturate the haemoglobin has not time to pass in 

 through the alveolar epithelium, just as occurs to a far greater 

 extent even during rest in a case of phosgene poisoning. 



Another possible explanation might perhaps suggest itself, and 

 seems, indeed, to be suggested in Chapter XI of Mr. Barcroft's 

 book, "The Respiratory Functions of the Blood." This is that the 

 velocity of the chemical reaction, which occurs when haemoglobin 

 comes into contact with oxygen at a certain partial pressure of 

 oxygen, is so low that there is not time for the change to complete 

 itself in the lungs during muscular exertion. The rate at which 

 haemoglobin takes up oxygen, or oxyhaemoglobin gives it off, 

 in presence of a certain partial pressure of oxygen is so extremely 

 rapid that at present we have no means of measuring it. We can 

 form some conception of what must be the velocity if we consider 

 what is happening in the circulation of a small warm-blooded 

 animal, such as a mouse or bird. As was shown by Dr. Florence 

 Buchanan-^^ the pulse rate of such an animal is, even during rest, 

 about 700 to 800 a minute. A volume of blood equal to the whole 



"Buchanan, Journ. of Physiol., XXXVII, Proc. Physiol. Soc, p. Ixxix, 1908; 

 and XXXVIII, Proc. Physiol. Soc, p. Ixii, 1909. 



