568 THE OUTGO OF ENERGY 



Reflex Augmentation. Count the human radi- 

 al pulse during four consecutive periods of fifteen 

 seconds. Let the subject sip cold water slowly. 

 Kepeat the count while the subject swallows. 



The frequency will be increased. 



Variations in the force and frequency of the 

 heart-beat follow the stimulation of most afferent 

 nerves, for example the central end of the divided 

 vagus, the sciatic, and other mixed nerves, the 

 nerves of special sense, and the afferent nerves 

 which arise in the heart and pass to the bulb. 



The most conspicuous of the nerves which bear 

 impulses from the heart to the central nervous 

 system in mammals is the depressor. This nerve 

 occurs as an isolated trunk in the rabbit, and is 

 found mixed with other fibres, for example in the 

 vagus, in many other animals. The stimulation 

 of the end of the severed depressor nerve in con- 

 nection with the heart is without effect. The 

 stimulation of the end in connection with the 

 bulb slows the heart and dilates the blood-vessels, 

 thus causing a great fall in the blood-pressure. 



THE INNERVATION OF THE BLOOD-VESSELS 



The Bulbar Centre. 1. Lightly etherize a large 

 frog. Expose and cut both vagus nerves (in 

 order to exclude inhibition of the heart). It is 

 of the first importance to avoid excessive hemor- 



