88 HOW TO WORK 



then passed down the tube and forced out at the lower opening. 

 The second piece of leather, c, is then put on, and fixed in its place 

 with another button, e. In the syringes now made for me by 

 Mr. Matthews, the piston consists entirely of metal. I have found 

 syringes of this description work exceedingly well, and the necessity 

 for re-leathering is obviated, but they are rather expensive. 



Pipes, of different sizes, to insert into the vessels, fig, 156. The 

 tubes of the smaller pipes should be made of silver. 



Corks, of the form represented in fig. 150, for the purpose of 

 plugging the pipes while the syringe is being filled with injecting fluid. 

 A stopcock, fig. 155, is also useful for the same purpose. 



forceps, of the form shown in fig. 149, which are known to surgical 

 instrument makers as bull's nose forceps, for stopping up any vessels 

 through which the injection may escape accidentally. 



A Needle, of the form of the aneitrism needle used by surgeons, 

 for passing the thread round the vessel to tie it to the pipe which is 

 inserted into it, fig. 158. This needle may be made of an ordinary 

 darning needle which has been carefully bent round after having been 

 heated in the flame of a lamp. The thread which is used should be 

 strong but not too thin, as there would be danger of its cutting 

 through the coats of the vessel. 



166. injection Cans. Size or gelatine is used as the material in 

 which the opaque colouring matter is suspended. It must be melted 

 in a water-bath and strained immediately before use. The copper 

 injecting can forms a very convenient apparatus for melting the 

 gelatine. There are five cans in the bath, represented in fig. 152, 

 pi. XXIII, so that injection may be very conveniently transferred 

 from one into the other, while all may be kept warm over an ordinary 

 lamp. 



The operation of injecting is described in page 98. 



Of Opaque Injections. 



Although by the old system of making opaque injections there is 

 no chance of making out new points in the structure of tissues and 

 organs, I shall give directions for making these injections, in case 

 some of my readers may desire to prepare specimens. The observer 

 must not, however, suppose that he will add much to existing 

 knowledge, however great an adept he maybe at this difficult process. 

 To make a perfect vermilion injection undoubtedly requires a 

 degree of skill -which any one may be proud to possess, but for all 

 that it is certain that little which has not been long since demonstrated 

 will be discovered by the process. 



167. The size should be of such a strength as to form a tolerably 



