RESPIRATION 169 



or increased. As a matter of fact the blood volume is usually much 

 increased in "anaemia," as was first shown by Lorrain Smith. 25 



It was found by Miss FitzGerald that in ordinary cases of 

 anaemia there is no appreciable diminution in the alveolar CO 2 

 pressure. 26 As will be shown more fully in Chapter VIII, a chronic 

 arterial anoxaemia, however slight, invariably lowers the alveolar 

 CO 2 pressure if time is given, and if the anoxaemia continues 

 during rest. The absence of a lowered alveolar CO 2 pressure in 

 cases of anaemia is thus clear evidence of the absence of anox- 

 aemia, in spite of greatly diminished oxygen-carrying capacity of 

 the blood. It is evident, therefore, that the circulation rate is much 

 increased in anaemia and this inference is confirmed by the ab- 

 sence of cyanosis. A little consideration will show that this in- 

 creased circulation rate, while it serves to maintain the normal 

 oxygen pressure of the blood in the systemic capillaries, will prob- 

 ably not reduce too much the pressure of CO 2 in the tissues. The 

 CO 2 conveying power of the blood in the living body depends, as 

 shown in Chapter V, on the concentration of haemoglobin present 

 in the blood, and this concentration is greatly reduced in anaemia. 

 Diminution in the actual CO 2 -conveying power of the blood in 

 the living body will therefore advance pari passu with the diminu- 

 tion of the oxygen-carrying power. Thus (as shown in Chapter 

 X) an increased circulation rate is brought about by the combined 

 stimulus of diminished oxygen pressure and increased CO 2 pres- 

 sure. This is not so in the case of anoxaemia from defective satura- 

 tion of the haemoglobin in the lungs ; nor, for the special reason 

 given above, in the anoxaemia of CO poisoning. The reason why 

 imperfect saturation of the arterial blood causes such serious 

 anoxaemia in the cerebrum and tissues elsewhere, while anaemia 

 causes so little anoxaemia (during rest) unless it is very extreme, 

 is probably bound up with this difference as regards effects on 

 CO 2 pressure in the tissues. The matter will, however, be discussed 

 more fully in Chapter X. 



The last cause of anoxaemia to be considered is that due prima- 

 rily to defective circulation ; and it will be referred to very briefly 

 here, as the relation of circulation to respiration will be discussed 

 in Chapter X. When the blood pressure is very defective owing to 

 failure of heart action or failing supply of venous blood to the 

 heart, the inevitable result is failure in the general circulation rate, 

 and failure also in the proper distribution of blood within the body. 



25 Lorrain Smith, Trans. Path. Soc. Lond., LII, p. 315. 

 86 Journ. of Pathol. and Bacter., XIV, p. 328, 1910. 



