PHYSIOLOGY. 45 



only. In the case of dysentery, the griping pains, which we 

 can prove to be in the colon, give the sensation of tenesmus 

 at the anus. I have added what may be called another piece 

 of theory, that the sensations are not only referred to a distant 

 part, but to a more sensible part. In some instances, I have 

 no doubt of explaining it in this way : The glans has indeed 

 more sensibility than the neck of the bladder; and we can hence 

 conceive why in the case of stone, or in gonorrhoea also, the 

 pain is felt more especially at that sensible part. But in other 

 cases, I cannot see that this should take place from the greater 

 quantity of nerves, or from their being more fully expanded ; in 

 these cases the sensation depends upon another circumstance : not, 

 strictly speaking, that the parts are more sensible, but that the 

 motion is in certain places rendered more considerable. You 

 must allow me the hypothesis here, that motions are pro- 

 pagated along the nerves, and that these are of the vibratory or 

 oscillatory kind. Now I say, that if an oscillation is propagated 

 along a nerve, so long as the course of the nerve is perfectly 

 free, the oscillation will not be accumulated ; but if there is a 

 stoppage, the oscillation will be accumulated there, and so its 

 force considerably increased. In this way I explain the many 

 instances of motions propagated till they arrive at a more sen- 

 sible part, or to an extremity, where a stop is put to the oscilla- 

 tions, as in the joints. Thus, the rheumatic affection of the hip- 

 joint is moved along the nerves ; and we have an obscure sensa- 

 tion which does not amount to pain, till it comes to the extremity 

 of the muscles, where they are fixed in the 'joints. Thus also 

 in the phenomena of electricity, when I receive the electric 

 shock in my two hands, it is felt most considerably in the wrists, 

 elbows, shoulders, &c." 3. As sensations usually arise from 

 impressions made upon the extremities of the nerves, and are 

 referred to these, so impressions made on the nerves in their 

 course, are sometimes referred to the extremities from whence 

 they had commonly arisen. " Here I have rather given the 

 fact than the explanation. But the fact is well known, that in 

 persons who have suffered the amputation of a leg or arm, the 

 sensations referred to the toes or fingers remain ; so that in the 

 case of explosions of guns, and such things as can affect the 



