SECT. XXXIX.6. i . GENERATION. 407 



probably a fenfibility, at the early (late of its exiftence ; and 

 muft be furnifhed with a nerve of fenfe, or of motion, to per- 

 ceive, and to felect, and to combine the particles, which com - 

 pofe the fluid it fecretes. And this nerve of fenfe which per- 

 ceives the different articles which compofe the blood, muft at 

 lead be conceived to be as fine and fubtile an organ, as the op^ 

 tic or auditory nerve, which perceives light or found. See 

 Sect. XIV. 9. 



But in nothing is this nice action of the extremities of the 

 blood- veflels fo wonderful, as in the production of contagious 

 matter. A fmall drop of variolous contagion diffufed in the 

 blood, or perhaps only by being inferted beneath the cuticle, 

 after a time, (as about a quarter of a lunation,) excites the ex- 

 treme veflels of the (kin into certain motions, which produce a 

 fimilar contagious material, filling with it a thoufand puftules. 

 So that by irritation, or by fenfation in confequence of irrita- 

 tion, or by affbciation of motions, a material is formed by the 

 extremities of certain cutaneous veflels, exactly fimilar to the 

 ftimuiating material, which caufed the irritation, or confequent 

 feniation, or aflbciation. 



Many glands of the body have their motions, and in confe- 

 quence their fecreted fluids, arTecled by pleafurable or painful 

 ideas, fince they are in many inftances influenced by fenfitive aflb- 

 eiations, as well as by the irritations of the particles of the pafling 

 blood. Thus the idea of meat, excited in the minds of hungry 

 dogs, by their fenfe of vifion, or of fmell, increafes the difcharge 

 of faliva, both in quantity and vifcidity ; as is feen in its hanging 

 down in threads from their mouths, as they (land round a din- 

 ner-table. The fenfations of pleafure, or of pain, of peculiar 

 kinds, excite in the fame manner a great difcharge of tears ; 

 which appear alfo to be more faline at the time of their fecretion, 

 from their inflaming the eyes and eye- lids. The palenefs from 

 fear, and the blufh of fhame, and of joy, are other inftances of 

 the effects of painful or pleafurable fenfations, on the extremi- 

 ties of the arterial fyftem. 



It is probable, that the pleafurable fenfation excited in the 

 ftomach by food, as well as its irritation, contributes to excite 

 into action the gaftric glands, and to produce a greater fecre- 

 tion of their fluids. The fame probably occurs in the fecretion 

 of bile; that is, that the pleafurable fenfation excited in the 

 ftomach, affects this fecretion by fenfitive aflbciation, as well as 

 by irritative aflbciation. 



And laftly it would feem, that all the glands in the body 

 have their fecreted fluids affected, in quantity and quality, by 

 the pleafurable or painful fenfations, which produce or accom- 

 pany 



