[ z6 9 ] 
of different lengths for different cafes. On the upper 
part of this canula there are two circles, each one of 
which is faften’d to a different piece. Thefe pieces 
are exhibited feparate in Fig. 4. and they are made fa 
as to be fcrew’d one on the other. Thefe circles are 
fomewhat concave in their furfaces, which correfpond 
reciprocally ; fo that their circumferences touch, 
while there is a tolerable vacuity towards their centre. 
By means of this fimple mechanifm, 1 apply the 
plafter x , with a hole in it, on the lower circle vf, 
whofe fcrew paffes into the hole of the plaifter : this 
done, I fcrew the upper piece B on the lower Jl, 
and I fqueeze the plaiffer tight between thefe two 
circles. The inffrument becomes then as in Fig. 5. 
The plaifter, which I have chofen, is that of Andreas 
a Cruce ; but one may ufe Burgundy-pitch, or any 
otherpowerful emplaftic, at pleafure. My plaiffer 
was three inches broad. To the upper end of the 
canula I adapted a very exadt filver fiopple r, Fig. 3. 
The part, where I intended to make the pundture, 
was fhaved, wider than the plaiffer. 
Thus having prepared every thing, and the canula 
being armed with its trocart, and fortified with the 
plaifter, as it appears Fig. y. I performed the punc- 
ture on Friday the 23 of Odtober 1744, by thrufting 
in the trocart and canula up to the circles and plaif- 
ter, which I applied and made to ffick in all its 
parts on the head, by preffing it with my hand and 
lingers made very warm, and alfo with hot linen- 
cloths. When the plaifter was thoroughly well 
faften’d on, I pull’d out the trocart, and drew four 
or five ounces of ferofity, of a brownifh white, or 
