CHAP, it.] RESPIRATION. 493 



repeated inspirations. The pauses become longer, and the 

 inspiratory movements shallower. Each inspiration is accom- 

 panied by the contraction of accessory muscles, especially of 

 the face, so that each breath becomes more and more a pro- 

 longed gasp. The inspiratory gasps spread into a convulsive 

 stretching of the whole body ; and with extended limbs, and 

 a straightened trunk, with the head thrown back, the mouth 

 widely open, the face drawn, and the nostrils dilated, the last 

 breath is taken in. 



Thus we are able to distinguish three stages in the phe- 

 nomena which result from a continued deficiency of air : (1) A 

 stage of dyspnoea, characterized by an increase of the respira- 

 tory movements both of inspiration and expiration. (2) A con- 

 vulsive stage, characterized by the dominance of the expira- 

 tory efforts, and culminating in general convulsions. (3) A 

 stage of exhaustion, in which lingering and long-drawn inspira- 

 tions gradually die out. When brought about by sudden occlu- 

 sion of the trachea these events run through their course in 

 about 4 or 5 minutes in the dog, and in about 3 or 4 minutes 

 in the rabbit. The first stage passes gradually into the second, 

 convulsions appearing at the end of the first minute. The 

 transition from the second stage to the third is somewhat 

 abrupt, the convulsions suddenly ceasing early in the second 

 minute. The remaining time is occupied in the third stage. 



The duration of asphyxia varies not only in different animals 

 but in the same animal under different circumstances. Newly 

 born and young animals need much longer immersion in water 

 before death by asphyxia occurs than do adults. Thus while 

 in a full-grown dog recovery from drowning is unusual after 

 1J minutes, a new-born puppy has been known to bear an 

 immersion of as much as 50 minutes. The cause of the differ- 

 ence lies in the fact that in the quite young or rather just born 

 animal the respiratory changes of the tissues are much less 

 active. These consume less oxygen, and the general store of 

 oxygen in the blood has a less rapid demand made upon it. 

 The respiratory activity of the tissues may also be lessened by 

 a deficiency in the circulation ; hence bodies in a state of syn- 

 cope at the time when the deprivation of oxygen begins can 

 endure the loss for a much longer period than can bodies in 

 which the circulation is in full swing. There being the same 

 store of oxygen in the blood in each case, the quicker circula- 

 tion must of necessity bring about the speedier exhaustion of 

 the store. So also anaesthetics may diminish the effects and 

 delay the final results ; large doses of anaesthetics may prevent 

 the exaggerated and convulsive movements. In many cases of 

 drowning, death is hastened by the entrance of water into the 

 lungs. 



By training, the respiratory centre may be accustomed to 



