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ployed all the preffure and force neceffary for turning the inftru- 
ment is applied by one hand of the operator, the faw is made 
to-cut by forming half a circle only, or fearcely fo much, and 
the perforation is finifhed by moving the faw backward and 
forward, till the whole thicknefs of the bone is divided ; but 
when the trepan is made ufe of, the Surgeon applies all the 
prefjure upon the head of the inftrument with one hand while he 
turns the handle of it with the other. Some operators indeed 
make the preffure upon it with their forehead, or with their 
chin, but it is more eafily and more equally applied with one 
hand, than it poffibly can be in any other manner; by the 
trepan the faw is made to move always in the fame direction, 
by which it cuts more eafily, and performs the operation in 
one-third of the time that is neceflary with the trephine; as it 
often happens that feveral perforations are neceilary, and as 
the operation is of confequence fatiguing to the operator and 
diftrefing to the patient, that method of operating ought furely to be 
preferred which renders the operation more eafy, provided it ‘is at 
the fame time equally fafe.” After having given this decifion in 
favour of the trepan, for expedition and fafety, he has taken 
motice, “ that fome practitioners, very fenfible of thefe advan- 
oe 
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tages of the trepan, but dreading the rifk of its paffing too /ud- 
denly in upon the brain, commence the operation with this in- 
{trument and finifh it with the trephine. This, he fays, is far 
preferable to the ufual method of performing the operation 
entirely with the trephine, but thofe who have fully experi- 
enced the advantages of the trepan will employ it for the 
whole operation.” . 
5S 2 I HAVE 
