BY DR. BURDON-SANDERSON. 317 



adult rabbit, the number of respirations per minute diminishes 

 from 120140 to 4050. That this is only to a very slight 

 extent dependent on the narrowing of the glottis due to the 

 relaxation of the intrinsic muscles of the larynx, is proved by 

 the fact that if the two recurrents are divided, the retarding 

 effect of the operation is very inconsiderable, while the re- 

 tarding effect of section is diminished in no appreciable degree 

 by previous tracheotomy. 2. The mechanism of breathing is 

 completely altered. Each respiration is about five times as 

 deep as it was before. This depends partly on increased action 

 of the diaphragm, partly on the participation of the accessory 

 muscles in the inspiratory act. The belly is projected and the 

 larynx drawn down by the sternal muscles in each inspiration, 

 while the upper ribs, which before were motionless, are drawn 

 upwards and outwards by the external intercostals and inter- 

 cartilaginous muscles. The inspiratory expansion of the 

 upper part of the thorax lasts for several seconds, at the end 

 of which it suddenly collapses, expelling the air with such 

 force as to make an audible sonorous noise in the air-passages, 

 often accompanied, if the trachea has not been opened, with 

 a coarse rale. This sudden collapse, which is a non-muscular 

 act, is followed by a long pause, the existence of which is 

 characteristic. At the end of it there usually occurs a short 

 expiratory movement, attended with hardening of the muscles 

 of the abdominal wall, which is the immediate precursor of the 

 inspiratory act. The mode of breathing just described is that 

 of dyspnoea; but there is this important difference between 

 ordinary dyspnoea and that produced by section of the vagi, 

 that whereas in the former the frequency of the respiratory 

 movements is increased, in the latter it is diminished ; with 

 this exception, all the characteristics of dyspnoea are present. 

 3. The quantity of air breathed per minute is as great after 

 section of both vagi as before, the diminished frequency of 

 the respirations being counterbalanced by the increased depth 

 of the respiratory act. This is proved by measuring the 

 quantity of air breathed in a given time in the manner above 

 directed. 4. These facts afford ground for inferring that 

 although section of both vagi does not materially either in- 

 crease or diminish the work done in a given time by the re- 

 spiratory muscles, it interferes veiy considerably with the 

 accomplishment of the purpose of their movements the ar- 

 terialization of the blood. Notwithstanding the vigor of the 

 respiratory movements, the blood becomes more or less venous. 

 101. Death after Section of both Vagi. Rabbits in 

 which both vagi have been divided, commonly die before the 

 end of the first day. Dogs live longer often two or three 

 days. After death, the lungs are found in an altered condi- 

 tion, of which the following are the leading features : The 



