Class I. 2. 2. 12. OF IRRITATION. 6<j 



cm Philofophical Society, Vol II. page 292, where a female one 

 is like wife described with nearly fimilar marks. 



The joining of the frontal bones, and the bregma, having been 

 later than that of the other futures of the cranium, probably 

 gave caufe to the whitenefs of the hair on thefe parts by delaying 

 or impeding its growth. 



1 2. Callus. The callous (kin on the hands and feet of laborious 

 people is owing to the extreme vefTels coaieicing from the per- 

 petual preflure they are expofed to. 



As we advance in life, the finer arteries lofe their power of 

 action, and their fides grow together ; hence the palenefs of the 

 feins of elderly people, and the lofs of that bloom, which is ow- 

 ing to the numerous fine arteries, and the tranfparency of the 

 ikin, that encloies them. 



M. M. Warm bath. Paring the thick (kin with a knife. 

 Smoothing it with a pumice ftone. Cover the part with oiled 

 filk to prevent the evaporation of the perfpirable matter, and 

 thus to keep it moid. 



13. Catarafta is an opacity of the cryftalline lens of the eye. 

 It is a diieale of light-coloured eyes, as the gutta ferena is of 

 dark ones. On cutting off with fciflars the cornea of a calf's 

 eye, and holding it in the palm of one's hand, fo as to gain a prop- 

 er light, the artery, which fupplies nutriment to the cryftalline 

 humour, is eafily arid beautifully feen 5 as it rifes from the cen- 

 tre of the optic nerve through the vitreous humour to the cryf- 

 talline. It is this point, where the artery enters the eye through 

 the cineritious part of the optic nerve, (which is in part near the 

 middle of the nerve,) which is without fenfibility to light ; as 

 is fhewn by fixing three papers, each of them about half an inch 

 in diameter, againft a wall about a foot diftant from each other, 

 about the height of the eye ; and then looking at the middle one, 

 withone eye, and retreating till you lofe fight of one of the exter- 

 nal papers. Now 2s the animal grows older, the artery becomes lefs 

 vifible, and perhaps carries only a tranfparent fluid, and atlenathin 

 fome {ubjecls I fuppofe ceafes to be pervious *, then it follows, that 

 the cryftalline lens, lofing fome fluid, and gaining none, becomes 

 dry, and in confequence opaque j for the fame reafon, that wet or 

 oiled paper is more tranfparent than when it is dry, as explained in 

 Clafs I. 1.4. 1 . The want of moifture in the cornea of old people, 

 when the exhalation becomes greater than the fupply,is the caufe 

 of its want of tranfparency ; and which like the cryftalline gains 

 rather a milky opacity. The fame analogy may be ufed to explain 

 the whitenefs of the hair of old people, which lofes its pellucidity 

 along with its moifture. See Clafs I. 2. 2. 11. 



M. M. Small electric fhccks through the eye. A quarter of 



a 



