168 PRACTICAL HISTOLOGY. 



completely filled by the injection, so that it contains 

 no bubble of air. To effect this, whilst the India- 

 rubber tube is kept closed by the strong spring clip 

 with which it is provided, the air in the apparatus 



Canulas for injecting. Natural size. 



c. 1 c. 2 , c.*, glass canulas of different sizes ; c. 4 , metal canula : it is sometimes 

 more easy to insert than the glass ones, especially into fine bloodvessels, or 

 into lymphatics ; cl, steel clip for clamping an artery, or a small India-rubber 

 tube; a and b are intended to illustrate the mode of making the glass ca- 

 nulas ; a, glass tube which has been heated in the middle in the blowpipe 

 flame, and drawn out so as to be narrower here ; b, the same tube after 

 having been again heated (by the tip of the flame), and drawn out at the 

 paints a; a;, so as to narrow it still more at those places The subsequent 

 proceeding consists in making a nick at I with the edge of a file, breaking 

 the tube across here, and with a fine, flat, wetted file grinding the end away 

 obliquely as far as the doited ring In each. The sharpness of the filed edije 

 is got rid of by inserting it for a moment or two in (he flame. Two similar 

 canulas are thus made from the one piece of tubing. 



is put under a pressure of about two inches of mer- 

 cury by working the syringe. The free end of the 

 India-rubber tube is now held up, and the clip 

 opened until the colored fluid forced up by the pres- 

 sure begins to escape, when the clip is immediately 

 closed and the tube is slipped on to the arterial 

 canula. The greatest care must be taken throughout 

 to avoid the introduction of air, since this would 

 obstruct the smaller vessels and prove fatal to the 

 success of the injection. 



The clip is now permanently opened and the injec- 

 tion suffered to flow into the aorta, at first under 

 the low pressure of two inches of mercury ; but the 



