ART. III. 2.1.2. SECERNENTIA. 33 



Other drugs have this double effect, and belong either to the 

 clafs of Secernentia or Sorbentia, according to the dofe in which 

 they are exhibited. Thus a fmall dofe of alum increafes ab- 

 forption, and induces coftivenefs -, and a large one increafes the 

 fecretions into the inteftinal canal, and becomes cathartic. And 

 this accounts for the conftipation of the belly left after the pur- 

 gative quality of rhubarb ceafes, for it increafes abforption in 

 a fmaller dofe, and fecretion in a greater. Hence when a part 

 of a larger dofe is carried out of the habit by ftools, the fmall 

 quantity which remains induces coftivenefs. Hence rhubarb 

 exhibited in fmall dofes, as two or three grains twice a day, 

 ftrengthens the fyftem by increafing the adtion of the abforbent 

 veflels, and of the inteftinal canal. 



2. Diaphoretics. The perfpiration is a fecretion from the 

 blood in its paflage through the capillary veflels, as other fecre- 

 tions are produced in the termination of the arteries in the va- 

 rious glands. After this fecretion the blood lofes its florid 

 colour, which it regains in its paflage through the lungs ; which 

 evinces that fomething befides water is fecreted on the {kins of 

 animals. 



No ftatical experiments can afcertain the quantity of our per- 

 fpiration ; as a continued abforption of the moifture of the at- 

 mofphere exifts at the fame time both by the cutaneous and pul- 

 monary lymphatic. 



3. Every gland is capable of being excited into greater exer- 

 tions by an appropriated ftimulus applied either by its mixture 

 with the blood immediately to the fecerning veflei, or applied 

 externally to its excretory duel:. Thus mercury internally pro- 

 motes an increafed falivation, and pyrethrum externally applied 

 to the excretory ducts of the falival glands. Aloes ftimulate 

 the rectum internally mixed with the circulating blood ; and 

 fea-falt by injection externally. Now as the capillaries, which 

 fecrete the perfpirable matter, lie near the furface of the body, 

 the application of external heat acts immediately on their excre- 

 tory ducts, and promotes perfpiration \ internally thofe drugs 

 which poflefs a fragant eflential oil, or fpiritus rector, produce 

 this effe6t, as the aromatic vegetables, of which the number is 

 very great. 



4. It muft be remembered, that a due quantity of fome 

 aqueous vehicle muft be given to fupport this evacuation ; oth- 

 erwife a burning heat without much vifible fweat muft be the 

 confequence. When the fkin acquires a degree of heat much 

 above 1 08, as appears by Dr. Alexander's experiments, no vifi- 

 ble fweat is produced ; which is owing to the great heat of the 

 fkin evaporating it as haftily, as it is fecreted ; and, where the 



fweat 



