390 RELATION OF RESPIRATION TO OTHER PROCESSES [CH. XXVII. 



In the second stage, which is not marked by any distinct line of 

 demarcation from the first, the violent expiratory efforts become 

 convulsive, and then give way, in men and other warm-blooded 

 animals, to general convulsions, which arise from the further stimula- 

 tion of the centres in brain and cord by venous blood. Spasms of 

 the muscles of the body in general occur, and not of the respiratory 

 muscles only. The convulsive stage is a short one, and lasts less 

 than a minute. 



The third stage, or stage of exhaustion. In it the respirations all 

 but cease, the spasms give way to flaccidity of the muscles, there is 

 insensibility, the conjunctivas are insensitive and the pupils are 

 widely dilated. Every now and then a prolonged sighing inspiration 

 takes place, at longer and longer intervals, until breathing ceases 

 altogether, and death ensues. During this stage the pulse is scarcely 

 to be felt, but the heart may beat for some seconds after the respira- 

 tion has stopped. The condition is due to the gradual paralysis of 

 the centres by the prolonged action of the venous blood. This stage 

 may last three minutes and upwards. 



After death from asphyxia it is found in the great majority of 

 cases that the right side of the heart, the pulmonary arteries, and 

 the systemic veins are gorged with dark, almost black, blood, and 

 the left side of the heart, the pulmonary veins, and the arteries are 

 empty. The explanation of these appearances may be thus summar- 

 ised : when oxygenation ceases, venous blood at first passes freely 

 through the lungs to the left heart, and so to the great arteries. 

 Owing to the stimulation of' the vaso-motor centres by the venous 

 blood, the arterioles, particularly those of the splanchnic area, 

 are constricted; the arterial blood-pressure therefore rises, and the 

 left side of the heart becomes distended. The highly venous blood 

 passes through the arterioles, and, favoured by the laboured respira- 

 tory movements, arrives at the right side of the heart, which it 

 fills and distends ; the right side of the heart is becoming feebler at 

 the same time, and therefore unable to effectively discharge its blood 

 through the pulmonary circuit. Simultaneously the left ventricle is 

 also becoming weakened, and therefore its suction action diminishes. 

 In this way the blood is dammed back in the right heart and 

 veins, and the left side of the heart therefore gets into the empty 

 condition in which it is found after death. Some consider that the 

 early onset of rigor mortis in the left ventricle may be in part a 

 cause of its contracted and empty condition. 



In the first and second stages of asphyxia, the arterial pressure 

 rises above the normal ; this is due to the constriction of the arterioles 

 which is in part produced by the suprarenal glands pouring out more 

 adrenaline into the circulation, owing to their being stimulated by 

 the excess of carbonic acid in the blood. The fall of pressure in the 



