PHYSIOLOGY. 57 



pains we have instances of stones of considerable size passing 

 from the kidneys to the bladder without much pain, while on 

 other occasions a very small stone will give the most exquisite 

 pain. In the one case the stone induces an irritation and con- 

 striction, by which the pain becomes considerable upon a small 

 distention. 



" It is highly probable that spasmodic constrictions take place 

 in the blood-vessels also, and have a considerable share in mo- 

 difying the pains which, as I formerly mentioned, arise from dis- 

 tention, and in producing the various sensations of impulse 

 which I noticed, (page 55.) You will now perceive that spasm 

 probably has a greater share than has been imagined in concur- 

 ring with, and modifying pains from distention. Thus, I refer 

 the pain from inflammation to distention by an increased impe- 

 tus in the part of the fluids, which are pushed on in greater 

 quantity, and with a greater velocity than that which the vessels 

 can admit ; but it is probable that neither the pain nor the ob- 

 struction would arise, if a spasm did not concur with the increas- 

 ed impetus of the fluids. 



" Another modification of pain which deserves notice, is that 

 which arises in parts where no external impression is made, in 

 consequence of impressions made upon distant parts, from which 

 they are propagated. (See LX. 2.) 



" PRURITUS. This symptom is very properly subjoined by 

 Gaubius, who calls it sensatio dolori proximo,. It is not pain, 

 but approaches to it : thus, certain chemical acrimonies give 

 only a pruritus, which arises to a certain degree of tickling ; in 

 a more concentrated state they produce smarting and pain. 

 The sensation of pruritus, however, does not always infer che- 

 mical acrimonies ; the vermes intestinales excite an itching at 

 the nose, which is no otherwise to be explained than by an 

 oscillation propagated along the whole alimentary canal and 

 fauces, till it reaches the more sensible part of the nose, where 

 the epithelium terminates. The same thing holds in the case 

 of calculi, and in the ardor urinse from gonorrhoea. 



" To the head of pain, and especially that of pruritus, Gaubius 

 adds a set of feelings, which belong to the appetites and pro- 

 pensities which I have enumerated in CXIX. 4 and 5. 

 They are frequently sensations sui generis, very often of 



