Sect. XXXIX. 6. i. GENERATION. 407 



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

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

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

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

 ceives the different articles which cornpofe the blood, muff at 

 leaf! be conceived to be as fine and fubtile an organ, as the op- 

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

 Sea. XIV. 9. 



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

 blood-veffels 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 vefTels of the fkin into certain motions, which produce a 

 iimilar contagious material, filling with it a thoufand puftules. 

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

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

 extremities of certain cutaneous veiTels, exactly fimilar to the 

 ftimulating material, which caufed the irritation, or confequent 

 fenfation, or aflbciation. 



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

 quence their fecreted fluids, affected by pleafurable or painful 

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

 ciations, as well as by the irritations of the particles of the palling 

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

 dogs, by their fenfe of vilion, 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 feniitive aflbciation, as well as 

 by irritative aflbciation. 



And laflly 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 



