ASPHYXIA. 363 



after a surprisingly long interval one more respiratory gasp fol- 

 lows, and with & gentle tremor the animal stretches itself in a 

 kind of tonic inspiratory spasm, after which it is no longer capa- 

 ble of resuscitation. This last pulseless stage to which the term 

 asphyxia is more properly confined is the most irregular in dura- 

 tion, but always the longest. 



The blood of an animal which has died of asphyxia is nearly 

 destitute of oxygen, the haemoglobin being in a much more re- 

 duced condition than is found in venous blood. The first and 

 most obvious effect produced by the circulation of blood so defi- 

 cient in oxygen is excessive stimulation of the respiratory centre, 

 which causes the extreme and varied actions just described. At 

 the same time the venous blood reaching the systemic arterioles 

 affects most profoundly the vasomotor mechanism, and causes a 

 rapid and considerable rise in blood pressure in the first stage of 

 asphyxia. The general constriction of the small arteries may be 

 brought about by the venous blood acting directly as a stimulus 

 to the medullary and spinal vasomotor centres, to the local 

 centres, or as direct stimulation of the muscle cells of the arteri- 

 oles themselves. The centres in the medulla which govern the 

 inhibitory fibres of the pneumogastric are also stimulated, and 

 consequently the heart beats more slowly. The increase in 

 arterial tension and the slow beat give rise to distention of the 

 ventricle, which, when a certain point is reached, impedes the 

 working of the heart, and its muscle begins to beat more and 

 more feebly, so that in the third stage the impulse can hardly be 

 felt. The muscular arterioles then become exhausted and relax, 

 the blood pressure falls rapidly, and with the death of the animal 

 reaches zero. Both sides of the heart and great veins are en- 

 gorged with blood in the last stage of asphyxia ; the cardiac 

 muscle, being exhausted from want of oxygen, is unable to pump 

 the blood out of the veins, or empty its cavity. 



Owing to the force of the rigor mortis of the left ventricle, and 

 the greater capacity of the systemic veins, the left side is found 

 comparatively empty some time after death, and at post-mortem 

 examination the right side alone is found overfilled. 



