252 



THE CIRCULATION OF THE BLOOD 



(broad) ; in the muscles of guinea pigs the diameter of the capillaries is 

 3.5 p, that of the corpuscles being 7.2 /*. In order that they may pass, the 

 corpuscles become folded, and the capillaries become deformed in shape, 

 as is shown in Fig. 79, which depicts several capillaries from the abdom- 

 inal wall of the guinea pig, after injecting india ink. The black particles 

 between the corpuscles indicate that these have been moving along during 

 the life of the animal. It will be observed that the corpuscles, in order to 

 force their way through the capillaries, become sausage-shaped as well as 

 being rolled in. It could be observed in living preparations in the frog 

 that the bloodflow is retarded when the deformation of the corpuscles is 

 great. These facts have naturally many most important applications. 



The great variability in the number of patulous capillaries according to 

 the activity of the tissues (muscles) shows that the oxygen supply must be- 



n 



. 7o L> 



Fig. 79. Capillaries from abdominal wall of guinea pigs after injection of india ink. The 

 black particles are absent from the corpuscles which will be seen to be distorted in shape. Note 

 that in a transverse section of a capillary the corpuscles may become folded. (Krogh.) 



come altered to meet the varying demands. Indeed Krogh has shown by 

 mathematical calculations based on: (1) the depth of actual muscle tissue 

 which each capillary supplies, (2) the rate of oxygen consumption and 

 (3) the diffusion rate of oxygen through tissues that the oxygen pressure 

 necessary to supply the muscle fibers is remarkably small, even during 

 the heaviest muscular work. This means that the oxygen pressure in the 

 muscular tissue must at all times be practically the same as that of the 

 venous blood, and that the call for oxygen by the tissues is readily met by 

 diffusion from the capillary blood. That a measurable pressure of oxygen 

 in the tissues is difficult to demonstrate does not contradict this conclusion 



