Class I. i. 2. 14. OF IRRITATION. 25 



manner as the fecretion of .tears is defigned to preferve the cor- 

 nea of the eye moift, and in confequence transparent ; yet has 

 this cutaneous mucus been believed by many to be an excre- 

 ment •, and I know not how many fanciful theories have been 

 built on its fuppofed obftruc~t.ion. Such as the origin of catarrhs, 

 eoughs, inflammations, eryfipelas, and herpes; 



To all thefe it may be fufficient to anfwer, that the ancient 

 Grecians oiled themfelves all over ; that fome nations have 

 painted themfelves all over, as the Pi£ts of this iiland ; that the 

 Hottentots fmear themfelves all over with greafe. And laftly, 

 that many of our own heads at this day are covered with the 

 flour of wheat and the fat of hogs, according to the tyranny of a 

 filthy and wafteful fafhion, and all this without inconvenience. 

 To this mult be added the ftrict, analogy between the ufe of the 

 perfpirable matter and the mucous fluids, which are poured for 

 fimilar purpofes upon all the internal membranes of the body ; 

 and befides its being in its natural ftate inodorous ; which is 

 not fo with the other excretions of feces, or of urine. 



The quantity of perfpirable matter being greater than that of 

 the excrementitious matters voided by (tool and urine, has been 

 ttfed as an argument in favour of its being an excrement 5 the force 

 of which I do not fee : but can readily underftand, that there 

 mult of neceffity be a great exhalation of a fluid which is ditfu- 

 icd over the whole external furface of the warm fkin, and per- 

 haps warmer Jungs* for the purpofe of keeping them moift and 

 pliant, and which is perpetually renewed as it evaporates ; but, 

 if it be conceived to be an excrement, there ieems to have been 

 no neceffity fot its quantity being fo great. 



The evaporation of this great quantity of fluid, fecreted on the 

 furface of the fkin and lungs, rnuft carry off much heat from 

 the body ; and as both this fecretion and confequent evaporation 

 will be in proportion to the activity of the cutaneous \4i7els, and 

 the heat occafioned by their increaied fecretion, it would feeoa, 

 that this evaporation of perfpirable matter is the caufe which. 

 preferves the animal body at the uniform degree of heat of 98 ; 

 in the fame manner as the evaporation of boiling water ^reierve* 

 it at 2 1 2 degrees of Farenheit's fcale. 



The peculiar ufe of the perfpirabie matter in preferving the. 

 membranes moift, which line the air-pipes of the lungs 3 appears? 

 from the curious difcovery of Dr. Priettley, that the oxygen 01" 

 the atmofphere will pafs through moift animal membranes, bin 

 not through dry ones, fo that if the membranes of the trachea 

 were to become drv. the animal muft as immediately perifh as 

 if he was to biearh u7o-ic eas alone. See Seel XXVUi, 2. of 

 the preceding voium 



vol. 11. [ in 



