NERVE-FIBRES AND NERVE-CELLS 127 



at regular intervals for hours together, and at every tap the 

 foot jerks forward. And if, by making the foot move a 

 pencil on a travelling cylinder, a record is kept of the ampli- 

 tude of the jerk, it is found to vary not only in harmony 

 with the subject's actions, but even with his emotions and 

 thoughts. This shows in a striking way the interdependence, 

 as opposed to the individualisation, of the several parts of 

 the central nervous system. 



Thirdly, we must call attention to an experiment, recently 

 performed, which puts Miiller's theory to a crucial test. 

 One nerve has at last been made to take the place of 

 another. The nerve for the face, which helps to regulate 

 the secretion of saliva and presides over blushing, dilation 

 of the pupil, erection of the hairs, etc. functions which ex- 

 plain the name of "little sympathetic " given to it long ago 

 starts from a ganglion in the upper part of the neck. Its 

 fibres therefore have their cells of origin in this ' ' superior 

 cervical ganglion" ; but the messages which pass through 

 its fibres are transferred to the ganglion-cells by a long 

 nerve, the roots of which come off from the dorsal part of 

 the spinal cord. The vagus nerve has been already alluded 

 to as the nerve of the heart, the stomach, and certain other 

 viscera. If the nerve which passes up the neck to the 

 superior cervical ganglion is cut out, and the vagus nerve is 

 also cut and turned round, the fibres of the latter reach out 

 along the track of the sympathetic nerve until they enter the 

 ganglion and surround its cells with their branches. Hence- 

 forth the vagus nerve, which ought to be supervising diges- 

 tion and the beating of the heart, controls blushing, dilation 

 of the pupil, and the other actions which formerly were 

 within the province of the cervical sympathetic. It is 

 unnecessary to point out how far-reaching are the conclusions 

 to be drawn from this experiment. It upsets our notions of 

 the specific functions of nerve-centres. It throws doubt 

 upon much that has been accepted as established knowl- 

 edge, and causes physiologists to pause and ask whether 



