INTRODUCTION. ig 
cess are represented in Fig. 1. The glass tubing is 
first held in the Bunsen flame until softened, and then 
pulled out gently to the form shown in A. After 
cooling a scratch is made with a file at the point indi- 
cated by the dotted line, the tube broken, and the end 
ground down obliquely to the form shown in B, upon 
a grindstone or a piece of ground glass. The narrow 
neck given to the cannula in this way is necessary in 
order to hold it firmly when tied in the blood-vessel. 
The two ends of the cannula should be slightly 
rounded by heating in the flame. If cannulas are 
needed for the smaller arteries, for ducts of the salivary 
eland, etc., the glass tube after being softened in the 
flame is pulled out to the proper diameter and then 
this narrowed portion is treated as above. 
The requisite features of a good cannula, especially 
‘if it is to be used in experiments upon a living animal, 
are that the neck should be as short as possible, and 
not any narrower than is necessary to enable the 
cannula to be tied firmly in the vessel; and secondly, 
the lip of the cannula should not be made too oblique, 
not more so than will facilitate its introduction into 
the vessel. Three of these cannulas will be required 
in the injection of the blood-vessels as described in 
Chapter IV., one for the aorta and two for the venz 
cave. As these must all be of large size they can 
easily be made. 
With reference,to the syringe, the hest. form un- 
doubtedly is the usual brass injection syringe provided 
with several brass cannulas and a stop-cock ; it can be 
obtained from any of the instrument-makers. These 
syringes, however, are very expensive, and those who 
cannot afford to buy them will find the common 
white-metal syringes with double leather piston a 
