DISTRIBUTED TO THE CAPILLARY VESSELS. 325 



which I have been led to accept. In the frog I have 

 succeeded in actually tracing nerve fibres from a 

 ganglion to a nerve trunk, and from the trunk to the 

 capillary vessels ; and in the bladder of the frog I 

 have been able to follow fine nerve fibres from the 

 ganglion both to arteries and capillary vessels. It 

 is surely justifiable to infer that a similar disposition 

 exists in the higher vertebrata and in man. Such 

 an inference is, however, almost irresistible if we bear 

 in mind the vast number of ganglia existing in the 

 submucous areolar tissue of the intestinal canal and 

 the course taken by the nerve fibres from these, and 

 the fact of the great alteration frequently taking 

 place in the vascular turgescence of the mucous 

 membrane. But, farther, there are certain physio- 

 logical experiments which have a most important 

 bearing' upon the question under discussion, and to 

 which I will direct the reader's attention. 



Physiological Experiments. — Many years ago when 

 I possessed two living specimens of the Proteus, 

 which I brought home from the cave at Adelsberg, I 

 often observed the change, which instantly took place 

 when a bright ray of light was suddenly thrown upon 

 the vessels of the exposed branchia?. The little arteries 

 of the giU suddenly contracted, and the entire volume 

 of the vascular tuft was reduced by at least one-third. 

 The circulation through the vessels was instantly 

 retarded, the diameter of the capillaries was sensibly 

 reduced, and the flow of the blood stream distinctly 

 checked. The ray of light, I conclude, acted directly 

 upon certain nerve fibres distributed around the 

 capillaries, and an impression being carried to the 

 nerve centre, the muscular fibre cells of the artery 

 were made to contract through the vaso-motor nerves 

 which are connected ^dth the same nerve centre. 



Another experiment which may be easily tried upon 

 the web of the foot of the living fi'og is almost as 

 conclusive, although it is open to the objection that 



