458 



PHYSIOLOGY 



CHAP. 



without previous suspension of respiration, or gradual alteration in 

 the transition from one type to another. The same effect appears 

 after cutting the second vagus, but in a more accentuated form ; 

 immediately after section the breaths become extremely dyspnoeic 

 and infrequent. In rabbit these effects are less marked than in 

 the dog, as appears from the curves of Fig. 211 (Luciani, 1879). 



-According to Gad (1880) these results are not simply the 

 expression of cutting out the vagus action on the respiratory 

 centres, since in dividing the nerve mechanical stimulation from 

 the operation is inevitable, as well as excitation from the demarca- 

 tion current set up in the injured trunk. He proposed to nullify 



FIG. 211. Effects of vagus section on respiratory rhythm on rabbits (AA') and dogs (BB'). 

 (Luciani.) The right vagi were cut at TI, the left at T%. In A and A' a large rabbit breathed 

 from a closed vessel, containing 12 litres of air. communicating with a writing tambour. 

 In B, B' a small dog breathed from a receiver of 30 litres air. 



the function of the vagus, by lifting it over a metal rod cooled 

 below zero, when the nerve would freeze suddenly at the point of 

 contact, and lose its conductivity, without producing excitation. 

 The results obtained with this more elegant method, however, 

 differed little from our own results with simple division, apart from 

 the fact that the inspirations alone became more ample, while the 

 expirations were maintained at the same height as before, or even 

 fell below it, as shown by Fig. 203. Even this difference was only 

 shown in the rabbit ; in the dog both inspirations and expirations 

 were increased.. 



These effects, which follow directly on the abolition of vagus 

 influence upon the respiratory centres, are not associated with any 



