The forceps was introduced only three times into the bladder for effecting the extraction of the three first stones, and only twice for the extraction of the fourth stone. Besides these four stones, which I have presented to the Society for their inspection, I thought it not improper to produce, at the same time, some other human _calculi_, for their further satisfaction, each of which was found single in the urinary bladders of different subjects. The surfaces of these stones may be observed to be much smoother than the surface of either of the four stones, that were extracted from Mr. Woodhams’s bladder in the operation I have just now recited; and therefore it was more reasonable to expect to find each of these stones accompanied with one or more stones in the same bladder (according to the received opinion), than it was to find more stones than one in the case of Mr. Woodhams’s, which has given rise to these observations. But as the fact before us does of itself shew the impropriety and danger of determining from the surfaces of such extraneous bodies, perhaps it may be thought needless to enlarge upon this subject, to strengthen those precautions so reasonable to be observed in this operation. However, as I have already taken notice of the smooth and polished appearances of the surfaces of such stones, as are probably never found single in the bladder; I have produced two stones of this kind, that were extracted from the same bladder, to shew, that these stones do no more resemble those stones of Mr. Woodhams’s, than a piece of polished marble can be said to resemble a rough block of the same species. _P. S._ I am informed, by a letter from Sussex, dated the 18th instant, that Mr. Woodhams is perfectly well in health; that the whole of his urine had passed through the urethra for the last five or six days; and that his wound will, in all probability, be soon healed. Joseph Warner. Hatton-Garden, February 22. 1758. [Illustration: _Philos. Trans. Vol. L._ TAB. XXII.(a) _p. 584_. Plate _is an exact representation of the sizes and external appearances of the four rough stones described in the preceding paper_ _J. Mynde sc._] LXXVII. _Observations on the_ Limax non cochleata Purpur ferens, _The naked Snail producing Purple. By_ John Andrew Peyssonel, _M. D. F.R.S. Translated from the_ French. [Read Feb. 23, 1758.]