E #ean J 
I wave been particular in reciting this paflage, as Mr. Bell (to 
whom the fcience of furgery is much indebted) has fo widely dif-. 
fered in his choice of the inftruments for perforating the fkull, 
from the opinion of Mr. Chefelden, Mr. Sharp, and Mr, Pott; 
but if we examine candidly the objections of Mr. Bell to the tre- 
phine (fome of which are certainly well-founded) we fhall find 
they may with equal juftice be applied to the trepan. If force or 
preffure be neceflary for the trephine, force and preffure muft 
furely be neceffary for the trepan; without a degree of preffure the 
inftrument cannot be kept in its place; for when the center-pin 
is removed is not, the part of the bone within the fulcus the cen- 
ter round which the faw muft turn? and if fome fort of preffure 
be not made on the knob, by the fuftaining hand, the faw cannot 
be retained in the furrow fo as to cut equally, but will with the 
leaft motion of the patient’s head be thrown out, by which the 
operation muft be retarded. The inftrument, by reafon of its 
length (few of them being lefs than eleven inches from the knob 
to the teeth of the faw, many of them more), cannot be replaced 
very expeditioufly ; it muft be admitted that it works quicker and 
more equably than the trephine; but though the trafine invented 
by John Woodall was made to cut in its motions backward and. 
forward, (that is, I fuppofe, the teeth of the faw fet alternately in 
oppofite direGiions) yet notwithftanding this mechanifm, that it is 
laborious and tedious every experienced Surgeon will allow; no 
doubt this was the reafon which induced many operators to begin 
the operation with the trepan for expedition, and finifh it with 
the trephine for fafety. 
In 
