EXCITATIONS IN SENSORY NERVES. 



231 



there is no nervous apparatus of perception. But if we can brino- this 

 extremity into relation with the perceptive centre, the brain we sliall 

 see whether there is sensation, which would imply centrifuo-al propa- 

 gation. 



The means employed in bringing about this condition of things is 

 very simple indeed. I remove, for the length of two or three centi- 

 metres, the skin from the tip of a young rat's tail, and insert the flayed 

 part into the subcutaneous cellular tissue through an oi^enino- made 

 in the skin of the animal's back. A few stitches suffice to hold the 

 parts in place, and soon they adhere firmly, the rat's tail then havinw 

 the ansate form. 



Fig. 1. Eat with Tip op Tail insektbd into the Dorsal Tissues. 



Eight months later I cut the tail in two, thus leaving two caudal 

 stubs. Immediately after section, the doi'sal stub was manifestly sen- 

 sitive; and when it was pinched vigorously, the rat would squeal and 

 run oiF. Hence it plainly appears that, in this fragment of a tail, the 

 excitation of the sensor nerves is propagated from the tiiick to the 

 slender end, or in a direction inverse to what is held to be the normal 

 course. The process was about as follows : the sensor nerves distrib- 

 uted to the extremity of the tail, on being wounded by the removal 

 of the skin, united with the sensor nerves of the dorsal region, which 

 in like manner had been cut into. In due coiirse of time the nerve- 

 cicatrix became able to transmit the shocks (whatever their nature) 

 which an excitation produces in a nerve. When, now, we pinch the 

 extremity of the dorsal stub, tlie shock is transmitted along the ex- 

 cited caudal nerve, passes through the cicatrix, and follows the dorso- 

 cutaneous nerve into the spinal marrow, which carries it to the brain, 

 where it results in a sensation of pain. 



The history of the case will be readily understood on examining 

 the following diagram, in which, for simplicity's sake, I have repre- 

 sented only one of the nerve-filaments of the tail {N C) and one of 

 the nerve-filaments of the back {D N). 



But this sensibility of the dorsal fragment begins to grow less on 



