xni RESPIRATORY RHYTHM 499 



The normal respiratory rhythm of man and other homothermic 

 animals in general is essentially conditioned by the reflex activity 

 of the centres. In eupnoea it is the established auto-regulation of 

 the vagi that predominates, i.e. the mode in which the air that 

 passes rhythmically through the lungs in a certain time is 

 distributed, depends on the rhythmical and alternate impulses 

 that reach the centres from the peripheral extremities of the 

 pulmonary vagi. The proof of this lies in the fact that normally 

 the nervous and muscular mechanisms of the thoracic movements 

 are always active ; inspirations alternate with expirations without 

 pause or intermediate rest (cf. tracings of Figs. 184, 185, 186, on 

 pp. 418, 420, 421), as if the excitation passed from the inspiratory 

 to the expiratory centres, and vice versa, by an uninterrupted 

 reciprocal, interceutral transmission, and with a delay that just 



Fi<;. -','<. Thoracic respiration of a soMinr, recorded with Marey's pn^uinouraiili 

 at 4"i60 niftivs. (A. Mosso.) 



suffices for the two antagonistic movements to succeed without 

 coincidence. 



Under certain special conditions, however, this perfect eupnoea 

 fails, probably in consequence of a diminished sensibility of the 

 afferent fibres of the vagi, which renders the impulse transmitted 

 to the inspiratory centres from, the expiratory position of the 

 lungs nil or inadequate. In this case there is between the end of 

 expiration and the commencement of inspiration a more or less 

 prolonged pause. This phenomenon, which we believe to be not 

 uncommon in clinical cases, was recorded graphically by Mosso in 

 two robust soldiers during rest upon the High Alps (4560 m. above 

 sea-level), as shown in the tracing of Eig. 235. We do not 

 interpret this as meaning that at high altitudes one breathes less, 

 since it is shown elsewhere that " at high altitudes no important 

 modifications in the output of carbonic acid and the intake of 

 inspired air occurs." Until the contrary is proved, we hold it 

 logical to assume that the phenomenon described depends upon a 



VOL. I '2 K , 



