292 RESPIRATION 



mals of the same species the blood volume is a function of the 

 ratio of body surface to mass, and even inferred that the carbon 

 monoxide method of determining blood volume (appendix) 

 must be incorrect because it showed no such relation in experi- 

 ments published by Douglas, ^^ The matter was afterwards re- 

 investigated in rats by Chisolm,^^ and by Boycott.*^ Figure 71 

 shows the results of Boycott and of Dreyer (all obtained by the 

 modified Welcker method) in rabbits of different sizes. It will 

 be seen that there is no difference between them, and that, al- 

 though young rabbits have usually a somewhat higher proportion 

 of blood than older ones, the increased proportion does not vary 

 with the proportion of body weight to surface. The circulation 

 rate must, other things being equal, be faster in a smaller animal 

 with its higher proportional metabolism, but an increased pro- 

 portional dead weight of blood would be no advantage, but a 

 disadvantage. 



When the volume of blood is reduced by considerable bleeding, 

 there is at first a fall in arterial, and doubtless also in venous, 

 blood pressure ; but soon the blood pressure is restored. The first 

 effect of the bleeding is probably to evoke partial compensation 

 by a pressor excitation of the vasomotor center. This is probably 

 due to diminished circulation rate and consequent fall in oxygen 

 pressure and increase of CO2 pressure in the medulla. Very soon, 

 however, the blood volume is more or less restored by taking up 

 of liquid from the tissues and intestines. The blood is thus diluted ; 

 but the diluted blood fills up the blood vessels and completely re- 

 stores the blood pressure. After a delay of many days or perhaps 

 several weeks, the hydraemic blood is restored to normal by re- 

 production of the missing corpuscles. 



Similarly when blood is transfused from another animal of 

 the same species there is at first a rise of both venous and arterial 

 blood pressure. Soon, however, the volume of blood is reduced 

 by disappearance of most of the extra plasma. The remaining 

 blood then contains an excess of red corpuscles, and these are only 

 got rid of in the course of some days or weeks. 



The changes which occur were followed by Boycott and Doug- 

 las with the help of the carbon monoxide method of determining 

 the blood volume in living animals. ^^ They found that on repeated 



"Douglas, Journ. of Physiol., XXXIII, p. 493, 1906. 



" Chisolm, Quart. Journ. of Exfer. Physiol., IV, p. 208, 191 1. 



"Boycott, Journ. of Pathol, and Bacter., XVI, p. 485, X912. 



"Boycott and Douglas, Journ. of Pathol, and Bacter., XIII, p. 270, 1909. 



