'204 HANDBOOK OF PHYSIOLOGY. 



veins are gorged with dark, almost black blood, and the left side of the 

 heart, the pulmonary veins, and the arteries are empty. The explana- 

 tion of these appearances maybe thus summarized: when respiration 

 is stopped, venous blood at first 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 

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

 particularly those of the splanchnic area, the blood-pressure rises and 

 the left side of the heart becomes distended. This latter effect may be 

 from the extra action of the right heart, but is more probably due to 

 the increased peripheral resistance, and its slower beat. Although the 

 arterioles are contracted, a little blood is allowed to pass through them, 

 and this highly venous blood, favored by the labored respiratory move- 

 ments, arrives at the right side of the heart. When it reaches the pul- 

 monary arterioles it gives rise to the same contraction in them as it did 

 in the systemic vessels. This obstruction to the circulation through 

 the lungs causes a distended condition of the right heart and the pul- 

 monary artery, and on the other hand, produces a greatly diminished 

 blood-flow through the pulmonary veins and to the left side of the heart, 

 resulting after a time in practical emptiness. So that in the third stage 

 of asphyxia it is stated by some observers that the left heart gets into 

 the condition in which it is found after death. Others think that the 

 empty condition of the left heart is a post-mortem phenomenon. In 

 the first and second stages of the condition the blood-pressure continu- 

 ously rises until it reaches a point far above the normal. The veins are 

 greatly engorged, so that when pricked they act as arteries, inasmuch as 

 they eject the blood for some distance. Both sides of the heart and the 

 pulmonary vessels are engorged with blood, at any rate during the 

 greater portion of these stages, and at the third stage blood-pressure 

 falls rapidly. 



Cause of death. The causes of these conditions and the manner in 

 which they act, so as to be incompatible with life, may be here briefly 

 considered. 



(1) The obstruction to the passage of blood through the lungs occurs 

 chiefly in the later stages of asphyxia, the obstruction being chiefly in 

 the arterioles, which contract under the influence of the vaso-motor 

 centre, or possibly of a special part of it, which governs the action of 

 the pulmonary blood-vessels. 



(2) Accumulation of blood, with consequent distention of the right 

 side of the heart and of the systemic veins, is the direct result, at least 

 in part, of the obstruction to the pulmonary circulation just referred to. 

 Other causes, however, are in operation, (a) The vaso-motor centres 

 stimulated by blood deficient in oxygen, cause contraction of all the 

 small arteries with increase of arterial tension, and as an immediate 



