UPON THE VASCULAR SYSTEM. 119 



tion. Considering that this distinguished physiologist long ago pointed out the 

 irritating effects upon certain nervous centres, which result from accumulation 

 of this substance in the blood, it is not surprising that he should have advanced 

 the above theory. The following experiment shows, however, that acceleration 

 of the pulse may follow section of the vagi although a hyperoxygenated con- 

 dition of the blood be maintained before and after the section. 



Experiment XIX. — In a strong rabbit I exposed the vagi, introduced a 

 canula into the trachea, and then by means of a special apparatus maintained 

 artificial respiration with such rapidity, that the respiration could be completely 

 stopped for twenty seconds without slowing of the heart ensuing. It was, 

 therefore, certain that a hyperoxygenated state of the blood had been fairly 

 produced.*" While care was taken to maintain the artificial respiration at the 

 same rate, I divided the vagi and watched the results for some time after. 

 They arethe following : — 



Time. 





Pulse in 15". 



5-12' 



Previous to Hyperoxygenation 



60 61 59 



„16' 



„ division of Vagi 



59 60 58 



„ 17' 14" 



Vagi divided 





22' 





65 64 64 



„2& 





66 64 65 



The above facts show that a quickened action of the pulse may follow section 

 of the vagi although the slightest approach to asphyxia is prevented. Further, 

 recent researches by Voit and RAUBERt prove, that until the pulmonary textures 

 undergo inflammation the increased depth of the respirations after division of 

 the vagi entirely compensates for their diminished frequency, so that the amount 

 of oxygen and carbonic acid in the blood undergoes no change. 



It is now generally believed that the acceleration of the pulse after division 

 of the vagi is due to escape of the heart from the restraining influence of these 

 nerves, and seeing that the acceleration very frequently follows the above- 

 mentioned lesion, it is inferred therefrom that the cardio-inhibitory fibres of the 

 vagi are in almost constant action. It occurred to me that if this explanation be 

 the true one, and the only one, we should expect to find no acceleration of the heart 

 follow division of the vagi after their cardio-inhibitory fibres have been paralysed 

 by such a substance as atropia. Accordingly, I performed a number of experi- 

 ments with a view to test this point ; but as these bear equally upon the 

 following question, I shall briefly allude to it before proceeding further. 



* Usually within three seconds after the respiration of a rabbit is arrested the heart comes almost 

 to a stand-still. This is due to irritation of cardio-inhibitory nerves by the asphyxiated condition of 

 the blood. 



f Centralblatt. 1868. No. 47. 



VOL. XXVI. PART I. 2 I 



