424 THE HUMAN BODY. 



expiratory muscles are more violent than those of the inspira- 

 tory. Thus undue want of oxygen at first merely brings 

 about an increased activity of the respiratory centre, and 

 especially of its expiratory division which is not excited in 

 normal breathing. Then it stimulates other portions (the 

 convulsive centre) of the medulla oblongata also, and gives 

 rise to violent and irregular muscular spasms. That the 

 convulsions are due to excitation of nerve-centres in the 

 medulla (and not, as might be supposed, to poisoning of the 

 muscles or of the fore parts of the brain by the extremely 

 venous blood) is shown of the facts (1) that they do not 

 occur in the trunk' of an animal when the spinal cord has 

 been divided in the neck so as to cut off the muscles from 

 the medulla; and (2) that they still occur if (the spinal cord 

 remaining undivided) all the parts of the brain in front of 

 the medulla have been removed. 



The violent excitation of the nerve-centres soon exhausts 

 them, and all, the more readily since their oxygen supply 

 (which they like all other tissues need in order to continue 

 their activity) is cut off. The convulsions therefore gradu- 

 ally cease, and the animal becomes calm again, save for an 

 occasional act of breathing when the oxygen want becomes 

 so great as to lead to efficient stimulation even of the dying 

 respiratory centre: these final movements are inspirations 

 and, becoming less and. less frequent, at last cease, and the 

 animal appears dead. Its heart, however, though gorged 

 with extremely dark venous blood still makes some slow 

 feeble pulsations. So long as it beats artificial respiration can 

 restore the animal, but once the heart has finally stopped 

 restoration is impossible. There are thus three distinguish- 

 able 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 dyspnoeic stage, more 



