TRACHEOTOMY TUBE AND TROCAR. 
95 
fairly meets them all, and, up to the point of our present experience, 
we think successfully masters them. T<f make this understood, 
we will now proceed to describe the different parts of which the 
tracheotomy tube and trocar is composed. 
Figure 1 is the SHIELD, in shape 
not very unlike that which used 
to be soldered into the end of the 
old tube. In Mr. Gowing’s in* 
strument it is free, and can either 
be slid upon the canula or taken 
off. When separated, it appears 
the thing depicted in the engrav- 
ing. It being, however, a sim- 
ple piece of thin mettle, some 
additional substance was needed 
to render it steady when placed 
in its proper situation. To gain 
this so far as was required, and at the same time avoid much 
additional weight round the central orifice, C, is a margin of some 
breadth, which effectually prevents the shield from shaking about 
or seeming unsteady, on account of the width of bearing which it 
presents. The shield fits the canula (Fig. 2), and in the wings are 
two slots or slits for the introduction of tapes or straps through 
them. Yet, supposing the shield to be put upon the canula, and 
to be tied around the neck of the horse, if it could not move to and 
fro, it nevertheless might slide up and down, for the margin that 
made it steady did not also render it stationary. To oblige it to 
retain one place, Mr. Gowing has re- 
sorted to a very simple but a very 
effectual plan. A is a pin and screw, 
which accurately fits a passage, B, 
within which a female screw is con- 
tained. A few turns of the head of 
the pin in one direction will therefore 
always enable the operator to tighten 
the shield upon the canula, and a few 
revolutions the contrary way will at 
any time empower him to shift the 
shield either backwards or forwards. 
Fig. 2. 
D 
