ASPHYXIA. .359 



The pupils of the eyes become widely dilated, the pulse cau 

 hardly be felt, aud the animal lies apparently dead, when often 

 after a surprisingly long interval one more respiratoiy gasp fol- 

 lows, and with a 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 passing through the systemic 

 capillaries affects most profoundly the vaso-motor nerve mecha- 

 nism, so as to cause 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 vaso-motor 

 centres, to the local centres, or as direct stimulation of the muscle 

 cells of the arterioles themselves. The centres in the medulla 

 which govern the inhibitory fibres of the pueumogastric are also 

 stimulated, and consequently the heart beats more slowly. The 

 increase in arterial tension and the slow beat give rise to disten- 

 sion of the ventricle, which, when a certain point is reached, im- 

 pedes 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 re- 

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

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

 engorged 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. 



