IN TROD UCTION: 1 3 



cess are represented in Fig. i. 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 

 gland, 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 venae 

 cavge. As these must all be of large size they can 

 easily be made. 



With reference to the syringe, the best 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 afl"ord to buy them will find the common 

 white-metal syrmges with double leather piston a 



