326 RESPIRATION. 



activity of the inhibitory centre always coincides with that of 

 minimum activity of the vasomotor centre. The experiment 

 l>3' which it is proved that the respiratory phases of arterial 

 pressure and pulse frequency are independent of the thoracic 

 movement, consists in curarizing a dog by the injection into 

 the venous system of a dose of curare only just sufficient to 

 paralyze the respiratory muscles (5 to 10 millig. for a dog of 

 10 Ibs. weight), and observing graphically the changes of ar- 

 terial pressure which occur during the gradual extinction of 

 the respiratory movements, with the aid of the apparatus de- 

 scribed above. The tracings, figs. 259-261, show what is ob- 

 served at three different stages of curarization. Curve 259 

 was drawn when the animal's muscles were still active. It 

 may be regarded as normal. Curve 260' corresponds to a 

 period at which each inspiration and expiration is represented 

 by a scarcel}' perceptible contraction and dilatation of the 

 chest. Curve 261 to a still later condition, in which the inspi- 

 ratory movements are indicated by a mere vibration of the 

 lever, produced (as was observed at the time) by momentary 

 contraction of certain inspiratory muscles which were not yet 

 completely paralyzed. We learn from these observations, that 

 during the gradual extinction of the respirator}' movements, 

 the intervals between them correspondingly lengthen ; and 

 that at first the variations of arterial pressure and pulse fre- 

 quency exhibit the characters which closely correspond to 

 those they exhibit normally. Subsequently, the ascents and 

 descents of the mercurial column become much more gradual, 

 and the changes of frequency less abrupt. Finally they as- 

 sume, so far as relates to arterial tension, the characters of the 

 variations known as Traube's curves, to be described in the 

 next paragraph. 



106. Traube's Curves. This term is applied by physio- 

 logists to the rhythmical variations of arterial pressure which 

 occur in curarized animals, after complete cessation of the re- 

 spiratoiy movements, and section of both vagi. They can be 

 demonstrated in the rabbit, cat, or dog, but most readily in 

 the last. Traube described them as they occur in the absence 

 of artificial respiration, i. <?., when the inflations are for a time 

 discontinued. During the gradual rise of arterial pressure 

 which, as we have already seen, takes place under those cir- 



1 In fig. 260 the notches in the lower tracing represent rudimentary 

 inspirations and expirations. The expiratory movements, e e e, are 

 only traceable, however, in the last half of the tracing ; they follow the 

 inspiratory, f i , at an interval of about five mill. = 1 sec. In fig.- 

 261. the expiratory movements are wholly indistinguishable. All the 

 tracings of this series are reduced one-half to save space. The distance 

 between the respiratory aud arterial tracing is also diminished for the 

 same reason. 



