PHENOMENA OF ASPHYXIA. 269 



itself is becoming more and more venous. This venous blood circulat- 

 ing in the medulla oblongata, and spinal cord stimulates the respiratory 

 centres, thus causing these violent respirations. This stage usually 

 lasts about a minute and gradually gives place to 



2. The second stage, when the inspiratory muscles become less active, 

 while those concerned in laboured expiration contract energetically, 

 and indeed almost every muscle in the body may contract ; so that 

 this stage of violent expiratory efforts ends in general convulsions. 

 The convulsions are due to stimulation of the respiratory centres by 

 the venous blood. The convulsive stage is short, and is usually reached 

 in a little over one minute. This storm is succeeded by 



3. The third stage, or stage of exhaustion, the transition being usually 

 somewhat sudden. This condition is brought about by the venous 

 blood acting on and paralysing the respiratory centres. The pupils are 

 widely dilated, consciousness is abolished, and the activity of the reflex 

 centres is so depressed that it is impossible to discharge a reflex act, 

 even from the cornea. The animal lies almost motionless, with flaccid 

 muscles, and to all appearance dead, but every now and again, at long 

 intervals, it makes a few deep inspiratory efforts, showing that the 

 respiratory centres are not quite, but almost paralysed. Gradually, the 

 pauses become longer and the inspirations feebler and of a gasping 

 character. As the venous blood circulates in the spinal cord it causes 

 a large number of muscles to contract, so that the animal 

 extends its trunk and limbs. It makes one great inspiratory 

 spasm, the mouth being widely open and the nostrils dilated, and 

 ceases to breathe. After this stage, which is the longest and 

 most variable, the heart becomes paralysed, partly from being 

 over-distended with venous blood, and partly, perhaps, from the 

 action of the venous blood on the cardiac tissues, so that the pulse 

 can hardly be felt. To this pulseless condition the term " asphyxia " 

 ought properly to be applied. In connection with the resuscitation of 

 asphyxiated persons, it is important to note that the heart continues to 

 beat for a few seconds after the respiratory movements have ceased. 



The whole series of phenomena occupies from 3 to 5 minutes, according 

 to the animal operated on, and depending also upon the suddenness 

 with which the trachea was closed. If the causes of suffocation act more 

 slowly, the phenomena are the same, only they are developed more slowly. 



The Circulation. The post-mortem appearances in man or in an 

 animal are generally well marked. The right side of the heart, the 

 pulmonary artery, the vense cava3, and the veins of the neck are 

 engorged with dark venous blood. The left side is comparatively 

 empty, because the rigor mortis of the left side of the heart, and the 

 elastic recoil of the systemic arteries, force the blood towards the 



