1867.] 



On the Ivfluence of Respiration on Circulation. 



393 



as to produce marked dyspnoea, and great exaggeration of the movements of 

 respiration, it was observed as distinctly as before that the increase of force 

 and frequency of the pulse were increased by the prolonged inspiratory 

 efforts of the animal. 



3. Experiments showing that when the respiratory cavity is completely 

 closed (as by plugging the trachea^, the relation between the respiratory 

 movements of the chest and the arterial pressure is reversed. — The pro- 

 cess of death by apnoea may be divided into two sta2;es ; the first extend- 

 ing from the moment of occlusion to the cessation of the struggles of 

 the animal and the supervention of apparent insensibility, the second ter- 

 minating with the extinction of the circulation. In order to observe the 

 characters of the respiratory movements and those of the heart during these 

 two stages, it was necessary to substitute a mercurial manom.eter for the 

 caoutchouc bag. It was then seen that at first the respiratory movements 

 increase in amplitude without altering in character ; but towards the end 

 of the first minute, when the animal begins to struggle, they become irre- 

 gular, and each struggle is accompanied by strong expulsive efforts, during 

 which the mercury in the dynamometer oscillates violently and rises to an 

 enormous height. At the commencement of the second stage, when the 

 animal becomes tranquil, the respiratory movements assume a different 

 character, become almost exclusively inspiratory (gasping), and much more 

 regular. They occur, however, at longer and longer intervals, until they 

 finally cease. iVs regards the relation between the oscillations of the two 

 manometers, the tracings show distinctly that throughout the wdiole pro- 

 cess they are strictly coincident, both as to the time of their occurrence and 

 their extent. Hence it may be concluded that the extraordinary elevation 

 of arterial pressure which has been long known to occur during the second 

 minute in death by apnoja, is not due, as was supposed by Dr. Alison and 

 Dr. John Heid, to obstruction of the capillary vessels, either pulmonary or 

 systemic, but to the violence of the respiratory efforts. The cavity of the 

 chest being closed, the force exercised by the respiratory muscles expresses 

 itself in variations of tension of the enclosed air, which are communicated 

 through the intra-thoracic arteries to those outside of the chest, pro- 

 ducing those violent oscillations of the dynamometer which have been re- 

 ferred to. 



In support of this inference, it was shown that in an animal under the in- 

 fluence of woorara (when all respiratory movement ceases, while those of 

 the heart are unaffected), the process of apnoea is not only of greater dura- 

 tion, but is not attended with any of those peculiar disturbances of the cir- 

 culation which have been hitherto attributed to capillary obstruction. The 

 gradual extinction of the force of the contraction of the heart is indicated 

 by a slow and uninterrupted subsidence of the arterial pressure. 



4. Experiments for the purpose of ascertaining inhovj far the infiuence 

 exercised by the respiratory movements on the heart in ordinary breathing 

 are cAemca?.*— For this purpose observations were made on animals which 



