CHAP, ii.] RESPIRATION. 377 



As time goes on, these inspiratory efforts become less frequent ; 

 their rhythm becomes irregular; long pauses, each one of which 

 seems a final one, are succeeded by several somewhat rapidly re- 

 peated inspirations. The pauses become longer, and the inspiratory 

 movements shallower. Each inspiration is accompanied by the 

 contraction of accessory muscles, especially of the face, so that 

 each breath becomes more and more a prolonged gasp. The in- 

 spiratory 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 phenomena 

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

 dyspnoea, characterized by an increase of the respiratory movements 

 both of inspiration and expiration. (2) A convulsive stage, charac- 

 terized by the dominance of the expiratory efforts, and culminating 

 in general convulsions. (3) A stage of exhaustion, in which lin- 

 gering and long-drawn inspirations gradually die out. When 

 brought about by sudden occlusion 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 difference lies in the 

 fact that in the quite young or rather just born animal the re- 

 spiratory changes of the tissues are much less active. These con- 

 sume 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 syncope 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 circulation must of necessity bring about the speedier 

 exhaustion of the store. 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 bear 

 a scanty supply of oxygen for a much longer time than usual 

 before dyspnoea sets in, as is seen in the case of divers. 



