566 THE OUTGO OF ENERGY 



one millimetre apart, stimulate the spinal cord 

 with a tetanizing current of a strength easily 

 borne on the tongue. 



Stimulation of the spinal cord will not inhibit 

 the heart. Stimulation of the cerebral hemi- 

 spheres will be also ineffectual. Now stimulate 

 the medulla oblongata. (Fig. 74.) 



The heart will be inhibited. 



This method of locating the cardio -inhibitory 

 centre is unsatisfactory, because the inhibition 

 produced may possibly be the result of the stimu- 

 lation of nerve paths to or from the centre. Its 

 results can be controlled by the method of suc- 

 cessive sections, to be explained in connection 

 with the vasomotor centre, page 565. 



The cardio-inhibitory centre is always in ac- 

 tion, for section of the vagi causes the heart to 

 beat more frequently. 



Augmentor Centre. It is probable that this 

 centre, like the inhibitory centre, is situated in 

 the bulb, but the location is not definitely known. 

 The constant activity of the augmentor centre is 

 shown by the fall in frequency of beat after sec- 

 tion of the vagi followed by bilateral extirpation 

 of the inferior cervical and first thoracic ganglia 

 in mammals. 



The neuraxons, or axis-cylinder processes, of 

 the augmentor cells lying in the central nervous 



