256 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



the other end and tied at h, A cannula for connecting an artery 

 with a kyinograpbion may either be of this sort, or may be 

 made of metal of the shape shown in Fig. 128a. As it is ditticult 

 to hold it with forceps, it should be put on a piece of wood or 

 whalebone of the sbape shown at B. This both holds it firmly, 

 and the point entering the vessel allows the cannula to be more 

 readily pushed on into the lumen. A few notches on the side 

 of the cannula prevent the vessel and ligature with which it has 

 been tied from slipping off the end. Ey means of the little ear 

 ai e, it can be tied to the tube, on to whicli it is fitted. 



Mode of Making Connulce, T-hthes, and Fens. — Cannuhie for 

 the trachea are made by closing one end of a tube, directing a 

 small blow-pipe fiame against a point in its side till it is quite 

 soft, and then suddenly blowing into it. The soft part expands 

 into a thin bulb, which is scraped off, and a hole remains in the 

 side of the tube. The object of this hole is to allow the air to 

 escape during expiration. Instead of a hole in the cannula, 

 one may be cut in tlie side of the india-rubber tube to wliich it 

 is connected ; but this is more apt to be accidentally closed. 

 Tlie tube is then drawn out into the form seen at Fig. 129a, 

 p. 262, cut off at both ends, and one end ground obliquely off 

 on a sandstone with some water. 



A knob may be made at the ends of other cannuLne for 

 various purposes, by heating the end and s jiiking it against a 

 piece of glass or iron, or by heating the end in a fiame, continu- 

 ing to blow steadily through the tube while you do so. 



T- tubes are made by blowing a hole in tlie side of one tube, 

 in the same way as for a respiration-cannula ; and then putting 

 the heated end of another tube over it while the first is still 

 hot, so that the two stick together. The joint must then be 

 annealed by heating it in an ordinary gas-flame, reducing the 

 size of the flame gradually, so that the glass may cool very 

 sh)wiy. 



Pens for use with a kymographion are made by drawing 

 tubes to a point, as shown in Fig. 128, E and F, and grinding the 

 point on a fine hone, and rounding it, if necessary, in the 

 flame. 



narcotising Animals. — Narcotics cannot be given in all cases 



