VOL. XL.] PHILOSOPHICAL TRANSACTIONS. 243 



layers or coats on the stalks of vegetables. And he had one formed round the 

 stone of that great plum, which comes pickled from thence, and is called 

 mango. 



As to the asperities or prickles on the rays, they were noticed, so long since 

 as the time of Cornelius Celsus, who, lib. T , c. 26, calls them calculi spinosi. 



It may seem very strange and paradoxical, what he can assert is true, that the 

 fewer the knobs, asperities, or prickles, are on the surface of calculi, the more 

 troublesome they are to the persons in whose bladders they lie. Dr. Hickes was 

 the most tormented with the stone in his bladder, of any he ever knew, espe- 

 cially on any motion. He would not submit to be cut for the distemper, on 

 account of his age, and many other reasons ; but ordered his executors, that 

 he should be opened after death, and the stone taken out of his bladder, put 

 into a silver box, and given to Sir Hans, who had been his physician for manj 

 years, to place it in his collection of such kind of curiosities. It is very parti- 

 cular in this stone, that the protuberances and prickles on it were few, and at a 

 distance from each other. Every one of them had made a hole in his bladder, 

 like a sheath or socket ; and when, upon motion, they were removed out of 

 their corresponding sheaths, they hurt the bladder in the sound parts, and put 

 him on the rack of pain. 



When they are thick-set, one hinders the other from entering or wounding 

 so deep; and perhaps gets not much farther than the mucus which lines the in- 

 side of the bladder. 



An Account of some Oil of Sassafras crystallized. By Mr. John Maud, F.R.S. 



N° 450, p. 378. 



Mr. M. observed that some essential oil of sassafras, which had stood exposed 

 to a frosty night, in an open vessel, was changed, 3 parts out of 4, into very 

 beautiful transparent crystals, 3 or 4 inches in length, half an inch in thick- 

 ness, and of an hexagonal form. 



These crystals subsided in water, were indissoluble in it, inflammable in the 

 fire, and when exposed to it, melted into their pristine state. Hence it was 

 evident, that they still retained the natural qualities of an oil, though they ap- 

 peared under a different modification of their constituent parts. 



What was most remarkable, was the metamorphosis from a fluid to a solid 

 body, of such a particular figure, and from a yellowish liquor, not unlike 

 Madeira wine, to a very pellucid body, like ice congealed from the most 

 transparent water. This seemed to afibrd a new instance of crystallization, 

 which being generally accounted for by the particles of a fluid, or those of any 



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