'Microscopical Essays, 



4*7 



them, being as it were more fhagreened than the exterior one, 

 •and lefs . tranfparent. The grains are not ftrongly united to each 

 other, but may be feparated without much trouble. Fig. 10, 

 Plate XXIII. A, reprefents a piece of fkin thus laid open. To 

 examine thefe particulars further, a piece of fkin a, Fig, g, was 

 laid in a few drops of water, on a piece of glafs, before the mi- 

 crofcope, and fome of the grains were feparated from it, as at b 

 c d, by preffing them with the point of a pin ; in endeavouring 

 to open them, they fpread themfelves into all parts of the water ? 

 and at 1 aft remained in heaps, as at e and £ 



If a polype is carefully placed before the mierofcope, without 

 wounding it, you will feldom be difappointed in feeing fome of 

 thefe grains detach themfelves- from the fuperficies thereof, and 

 that even in the moft healthy. 



But if the grains feparate themfelves in large quantities, it is the 

 fymptom of a very dangerous diforder ; the furface of the polype 

 thus attached becomes more and more irregular, and is no longer 

 well terminated and defined as before. The grains fall off on all 

 fides, the body and arms contract and dilate, it becomes of a 

 white mining colour, lofes it's form as at a, Fig. 4, Plate XXIII. 

 A, and then diflblving into a heap of grains, as at b, Fig. 5. 

 The progrefs of this diforder is moft eafily obferved in the hydra, 

 viridis-.. 



A very attentive and accurate examination (hews that the fkin 

 is formed of a kind of glarous fubftance, a fpecies of gum, which 

 iil Is up the intervals between the grains, in which they are 

 lodged, and by which they are attached (though weakly) together. 



