ASPHYXIA. 401 



and the animal appears dead. If, however, its chest be 

 opened the heart will be found gorged with extremely dark 

 Tenons blood and making its last few slow feeble pulsations. 

 So long as it beats artificial respiration can restore the ani- 

 mal, but once the heart has finally stopped restoration is 

 impossible. There are thus three distinguishable stages 

 in death from asphyxia. (1) The stage of dyspnoea. (2) 

 The stage of convulsions. (3) The stage of exhaustion; the 

 convulsions having ceased but there being from time to 

 time an inspiration. The end of the third stage occurs in 

 a mammal about five minutes after the oxygen supply has 

 been totally cut off. If the asphyxia be due to deficiency, 

 and not absolute want, of oxygen of course all the stages 

 take longer. 



Circulatory Changes in Asphyxia. During death by 

 suffocation characteristic changes occur in the working of 

 the heart and blood-vessels. The heart at first beats 

 quicker, but very soon, before the end of the dyspnceic stage, 

 more slowly, though, at first, more powerfully. This slowing 

 is due to the fact that the unusual want of oxygen leads to 

 stimulation -of the cardio-inhibitory centre in the medulla 

 (p. 250) and this, through the pneumogastric nerves, slows 

 the heart's beat. Soon, however, the want of oxygen affects 

 the heart itself and it begins to beat more feebly, and also 

 more slowly, from exhaustion, until its final stoppage. 

 During the second and third stages the heart and the venae 

 cavae become greatly overfilled with blood, because the 

 violent muscular contractions facilitate the flow of blood 

 to the heart, while its beats become too feeble to send it 

 out again. The overfilling is most marked on the right 

 side of the heart which receives the venous blood from the 

 Body generally. 



During the first and second stages of asphyxia arterial 

 pressure rises in a marked degree. This is due to excitation 

 of the vaso-motor centre (p. 254) by the venous blood, and 

 the consequent constriction of the muscular coats of the 

 arteries and increase of the peripheral resistance. In the 

 third stage the blood-pressure falls very rapidly, because 

 the feebly acting heart then fails to keep the arteries 



