298 RESPIRATION 



amount of haemoglobin in the body. The characteristic dyspnoea 

 and faintness on exertion in chlorosis, etc., are probably due to 

 the impossibility of sufficiently increasing during exertion the 

 already greatly increased circulation. 



In pernicious anaemia and the anaemia of haemorrhage, Lor- 

 rain Smith found a very marked diminution of the total haemo- 

 globin present ; but often enough the blood volume was increased 

 above normal. 



Although the intimate connection between breathing and cir- 

 culation is already very evident, many points in the connection 

 are still uncertain or obscure. There is an abundant field for 

 clinical and physiological investigation in elucidating this sub- 

 ject, though it must always be remembered that not only are 

 breathing and circulation closely dependent on one another, but 

 they are dependent also on other physiological activities. 



Addendum. The experiments by Douglas and myself on the 

 regulation of the circulation in man have now been completed, and 

 are in course of publication. A very complete series, in which 

 Douglas was himself the subject, shows that during complete rest 

 the mixed venous blood had only utilized about 19 per cent of its 

 available oxygen, and gained a corresponding charge of CO2. 

 During hard work, with the oxygen consumption increased about 

 nine times, about 65 per cent of the arterial oxygen was utilized. 

 The pulse rate was increased about 2.6 times, and as the utiliza- 

 tion of the arterial oxygen was increased 3.4 times, the output of 

 blood per heartbeat was practically the same during hard work 

 as at complete rest, and the blood flow had simply increased in 

 proportion to the increase of pulse rate. 



Various other subjects, including myself, had a similar high 

 rate of blood flow (about 8 liters per minute) during rest, but one 

 or two had a markedly lower rate of flow, with the percentage 

 utilization of oxygen as high, in one case, as 33 per cent. In this 

 case the output per beat during rest, and the circulation rate (about 

 4.7 liters per minute) were a good deal lower than in the other 

 subjects, but the output per beat increased to about double during 

 hard work. There are thus considerable individual differences 

 (quite apart from differences in weight) as regards the rate of 

 general blood flow and the particular manner in which the circu- 

 lation adapts itself to varying amounts of work. 



As some doubt has arisen lately as to whether oxygenation of 

 blood within the living body has the same influence on the CO2 



