THE EESPlRATORr SYSTEM. 399 



though even in this animal there are variations in this respect 

 with the breed, age, etc. 



The Respiration and Circnlation in Asphyxia.— A most in- 

 structive experiment may be arranged thus : 



Let an ansesthetized rabbit, cat, or such-like animal, have 

 the carotid of one side connected with a glass tube as before 

 described (pages 328, 329), by which the blood-pressure and its 

 changes may be indicated, and, when the normal respiratory 

 acts have been carefully observed, proceed to notice the effects 

 on the blood-pressure, etc., of pumping air into the chest by a 

 bellows, of hindering the ingress of air to a moderate degree, 

 and of struggling. With a small animal it will be difficult to 

 observe the respiratory eflPects on the blood-pressure by simply 

 watching the oscillations of the fluid in the glass tube, but this 

 is readily enough made out if more elaborate arrangements be 

 made, so that a graphic tracing may be obtained. 



But the main events of asphyxia may be well (perhaps best) 

 studied in this manner : 



Let the trachea be occluded (ligatured). At once the blood- 

 pressure will be seen to rise and remain elevated for some time, 

 then gradually fall to zero. These changes are contemporane- 

 ous with a series of remarkable manifestations of disturbance 

 in the respiratory system as it at first appears, but in reality 

 due to wide-spread and profound nutritive disturbance. So far 

 as the breathing is concerned, it may be seen to become more 

 rapid, deeper, and labored, in which the expiratory phase be- 

 comes more than proportionably marked (dyspnoea) ; this is fol- 

 lowed by the gradual action of other muscles than those usually 

 employed in respiration, until the whole body passes into a ter- 

 rible convulsion — a muscle-storm in consequence of a nerve- 

 storm. When this has lasted a variable time, but usually 

 about one minute, there follows a period of exhaustion, during 

 which the subject of the experiment is in a motionless condi- 

 tion, interrupted by an occasional respiration, in which inspi- 

 ration is more pronounced than expiration; and, finally, the 

 animal quietly stretches every limb, the sphincters are relaxed, 

 there may be a discharge of urine or fseces from peristaltic 

 movements of the bladder or intestines, and death ends a strik- 

 ing scene. These events may be classified in three stages, 

 though the first and second especially merge into one another : 

 1. Stage of dyspncea. 2. Stage of convulsions. 3. Stage of 

 exhaustion. 



