38 PHYSIOLOGY. 



terposcd substances ; in other cases there may be a singular 

 tenuity of the cuticle, &c. to which may be imputed an increased 

 sensibility." 2. The different state of the medullary substance 

 of the sentient extremities, as given to it in the original stamina. 

 " Whenever we observe any state of the functions, which is 

 respectively the same throughout the whole of life, and continues 

 so under a considerable variety of external circumstances, we 

 say it depends upon the whole habit upon the constitution ; 

 and this carries us up to the state of the original stamina. It is 

 acknowledged by all physicians, that there is a difference of 

 sensibility which runs through the whole of life in one sex more 

 than in the other. It is proper to be observed that this gives 

 a seminium or predisposition to disease; and when this is 

 excessive, it has a considerable share in the most remarkable 

 affections of the nervous system. We would be curious to 

 inquire in what consists this constitution of the original stam- 

 ina, which remains in its effects through the whole of life : 

 we have little hopes, however, of solving this problem, and 

 would wish to limit it, and inquire, whether it consists in the 

 animal solid part of every medullary fibre, or in the different 

 conditions of what we suppose an inherent fluid there. It is pro- 

 bable that these two are connected, but we are disposed to believe 

 that it is in the state of the simple solid substance." 3. The 

 different state of tension in the medullary substance of the 

 sentient extremities, as given to it by the state of the blood- 

 vessels constantly connected with it. " This is a point of some 

 curiosity, and has not been hitherto noticed by any of our phy- 

 siologists. In considering (XLVIII.) the continuance of 

 sensations after the action of the external body has ceased, I 

 alleged that the motion excited in the sentient extremity must 

 be of the oscillatory or vibratory kind, somehow depending 

 upon an electric tremor. But if there is any truth in this, a 

 certain degree of tension is necessary to these oscillations ; so 

 that it is possible that the state of the sentient extremities may 

 be varied by different states of tension. The difficulty is to 

 understand how this state of tension is given to them ; and I 

 think it must be referred to the state of the blood-vessels 

 which accompany them. Nothing is more remarkable than the 

 uncommon number of blood-vessels intermixed with the sentient 



