370 



RESPIRATION. 



[CH. XXIV. 



passes freely through the lungs to the left heart, and so to the 

 great arteries. When it reaches the arterioles either by its 

 direct action upon their muscular tissue, or more probably 



Fig. 329. The heart in the first stage of asphyxia. The left cavities are seen to be 

 distended ; the left ventricle partly overlaps the right. La., left auricle ; l.v., left 

 ventricle ; a, aorta ; p. a., pulmonary artery ; p.v., pulmonary vein ; r.a., right auricle ; 

 r.v., right ventricle ; v.c.d., descending vena cava; v.c.a., ascending vena cava. (Sir 

 George Johnson.) 



through the medium of the vaso-motor centres, the arterioles 

 contract, particularly those of the splanchnic area, the blood- 



Fig. 330. The heart in the final stage of asphyxia. The letters have the same meaning as 

 in fig. 329 ; in addition, p.c. represents the pulmonary capillaries. The right auricle 

 and ventricle, and the pulmonary artery, are fully distended, while the left cavities of 

 the heart and the aorta are nearly empty. (Sir George Johnson.) 



pressure rises, and the left side of the heart becomes distended. 

 Although the arterioles are contracted, the highly venous blood 

 is allowed to pass through them, and, favoured by the laboured 



