1821.] Dr, Yellowfy on Dr. Prout's Estimate of Mortality. 363 



Article VI. 



Observations on Dr. Front's Estimate of Mortality from the 

 Operation of Lithotomy. By John Yelloly, MD. tRS. 8cc. 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, Car rozo Abbey, Nortolch, March 30, 1821. 



I BEG to notice, through the Annals of Philosophy , an inac- 

 curacy into which Dr. Prout has inadvertently fallen, in the 

 statement which he has given, in his valuable work on the 

 Diseases of the Urine,^ of the mortality occurring in the opera- 

 tion of lithotomy, in the Norfolk and Norwich Hospital; and in 

 the deduction which he has made, as to the mean ratio of morta- 

 lity fi-om that operation, over the whole kingdom. 



Dr. Prout quotes Dr. Marcet's published account of the cases 

 which occurred in the Norfolk and Norwich Hospital up to 

 1816,t and infers, that as the mortality which took place in indi- 

 viduals below puberty, was 1 in 18, while that in adults, was 1 in 

 4f, the mortaUty of the whole must be 1 in 11|-, or the mean 

 between the two proportions. 



It is obvious, however, that this calculation could only be 

 correct, if the number of deaths at those two respective periods 

 were equal ; but as this is not the case, the mean ratio can only 

 be obtained, by dividing the whole number of cases, by the v/hole 

 number of deaths, which Dr. Marcet does, and thus gives the 

 mortality as 1 in 7^, the deaths being 70 in 506 cases. 



Taking this as the accurate proportion of deaths in the Norfolk 

 and Norwich Hospital, up to the year 1816, (which, from my 

 own inspection I can state to be the case,) the proportional mor- 

 tahty, from the operation of lithotomy in the whole kingdom, as 

 inferred by Dr. Prout, from the mean of that in the Bristol, 

 Leeds, and Norwich Hospitals, will be about 1 in 6^, instead of 

 1 in 7|-, which he states it to be. 



I remain, dear Sir, yours sincerely, 



J. Yelloly. 



* Page 2i8. -j- Marcet on Calculous Disorders, p. S6. 



