CH. XXI.] CLAUDE BERNARD'S EXPERIMENT. 307 



nerves when one wishes to ascertain their functions. They consist 

 of section and excitation. 



Section of a vase-constrictor nerve, such as the splanchnic, 

 causes a loss of normal arterial tone, and consequently the part 

 supplied by the nerve becomes flushed with blood. Stimulation 

 of the peripheral end causes the vessels to contract and the part 

 to become comparatively pale and bloodless. This can be very 

 readily demonstrated on the ear of the rabbit. This is a classical 

 experiment associated with the name of Claude Bernard. Division 

 of the cervical sympathetic produces an increased redness of the 

 side of the head, and looking at the ear, the transparency of which 



fig. 288. Tracing showing the effect on blood -pressure of stimulating the central end of 

 the Depressor nerve in the rabbit. To be read from right to left. T, indicates the 

 rate at which the recording-surface was travelling, the intervals correspond to seconds ; 

 C. the moment of entrance of current ; O, moment at which it was shut off. The 

 effect is some time in developing, and lasts after the current has been taken off. The 

 larger undulations are the respiratory curves ; the pulse oscillations are very small. 

 (Foster.) 



enables one to follow the phenomena easily, the central artery 

 with its branches is seen to become larger, and many small 

 branches not previously visible come into view. The ear feels 

 hotter, though this effect soon passes oft' as the exposure of a large 

 quantity of blood to the air causes a rapid loss of heat. On 

 stimulating the peripheral end of the cut nerve, the ear resumes 

 its normal condition and then becomes paler than usual owing to 

 excessive constriction of the vessels. 



The first part of the experiment, the dilatation following 

 section, can be demonstrated in a very simple way, by pressing 

 the thumb-nail forcibly on the nerve where it lies by the side of 

 the central artery of the ear. 



Section of a vaso-dilatator nerve, such as the chorda tympani, 



X2 



