When dining at Passy some weeks ago I heard you mention that fixed Air had been used with success as a dissolvent in some Case or Cases of a Stone in the bladder. An Acquaintance of mine here desirous to try its power in some Cases now under his care wishes to collect every attainable information on the subject. I cannot doubt your contributing what you can to so good a purpose. A recital of what may have come to your knowledge in this matter, or an Indication where particulars of the Cases you alluded to may be gained will oblige Sir Your most humble Servant