Dr. Wollaston on Cystic Oxide, 
and consequently very soon separated.* This species is pro- 
bably very rare ; for, although I have omitted no opportunity 
of paying attention to any urinary concretions to which I could 
have access, I have, to this time, seen only one other specimen 
of the same substance. This last is in a collection of calculi 
belonging to Guy’s Hospital, given by Mr. Lucas, surgeon 
to that Institution, having been formed partly by his father, 
and partly by himself, in the course of their practise ; and 
according to the present arrangement, (which, it is to be hoped, 
will not be altered) the calculus to which I allude may be 
found by reference to No. 46 of that collection. It was ex- 
tracted by the usual operation, from a man 3 6 years of age, 
of whom no record is preserved, except that his name was 
William Small. It weighed, when entire, 270 grains. 
In appearance, these calculi resemble more nearly the triple 
phosphate of magnesia, than any other calculus ; but they 
are more compact than that compound is usually found to be : 
not consisting of distinct laminae, but appearing as one mass 
confusedly crystallized throughout its substance. Hence, 
instead of having the opacity and whiteness observable in 
fusible calculi, which consist of a number of small crystals 
cemented together, these calculi have a yellowish semi-trans- 
parency ; and they have also a peculiar glistening lustre, like 
that of a body having a high refractive density. 
When this substance is submitted to destructive distillation, 
* I am informed, that another stone formed afterwards in the bladder of this boy, 
and that he died in consequence, without submitting to the operation a second time. 
The stone found in his bladder after death, consisted principally of uric acid, but 
was peculiar in one respect, as its center was hollow by the removal of some more 
soluble substance, of which the nucleus had consisted. 
