170 THE MICROSCOPE 



of the larger bottle, a piece of flexible tubing is carried to the 

 shorter bent tube in the smaller bottle, and attached to the longer 

 bent tube in the smaller bottle is a flexible tube with a nozzle 

 which will fit the stop-cock tube fitted into the cannula. The 

 smaller bottle is filled with injection fluid, and both corks are 

 fitted. The stop-cock in the short tube bent at right angles (in 

 the larger bottle) is closed, and the tin vessel gradually raised ; the 

 water runs out into the larger bottle by the tube passing to the 

 bottom ; the air in this large bottle is gradually compressed, and 

 is driven into the smaller bottle, and the increase of pressure 

 drives the fluid out of the bottle and into the vessels which are to 

 be injected. 



The pressure in the vessels is indicated by the mano- 

 meter, and is very readily regulated by merely raising or 

 lowering the tin from which the water gets its " head," or by 

 regulating the amount of water flowing from the main. The 

 pressure should commence at |- inch of mercury, and be very 

 gradually raised to 3 or 4 inches, according to the nature of the 

 organ or tissue which is to be injected. Where the gelatine 

 injection is used, the organ and the bottle containing the fluid 

 must both be placed in a vessel of water, which should be 

 maintained at a constant temperature of about, but never above, 

 104° F. (40° C.) for an hour before the injection, and during the 

 time the injection is running. N.B. — Always fill the tubes with 

 the injecting fluid before attaching to the cannula (the cannula 

 having been already filled), in order that no air may get into the 

 vessels. 



Before proceeding to inject arrange the following instruments : 

 — the syringe, thoroughly clean and in working order, with pipes, 

 stopcocks, and corks shaped to stop the pipes while refilling the 

 syringe, a few scalpels, scissors, dissecting forceps, bull's nose 

 forceps for stopping up any vessel through which the injection 

 may escape accidentally, an aneurism needle for passing threads 

 round vessels, wash-bottle, floss silk or oiled worsted, and injecting 

 fluid. 



Killing the Animal to be Injected. — This is most easily done by 

 opening it from anus to throat, and cutting deeply into the heart 

 across the right auricle. It is, of course, done whilst under 



