118 VASCULAR SYSTEM. 



with two pairs of dissecting forceps as far down as possible. 

 A ligature having been passed round the vessel and looped, 

 and the vessel slit open, the canula is introduced and the 

 ligature tightened. The canula having been then cleared, of 

 blood and filled with saline solution, the plate on which the 

 animal lies is put into the warm chamber which contains the 

 injection bottle. This bottle, which is charged with the warm 

 Prussian blue mas?, is connected with the pressure bottle, the 

 manometer of which indicates a pressure of 60 to 120 milli- 

 metres. It is, however, not in communication with it, for the 

 connecting tube is closed by a clamp. This clamp is then 

 slightly opened for a moment, so as to fill the discharge tube 

 to the orifice, and immediately closed, the stopcock being 

 shut at the same time. The nozzle having been inserted into 

 the canula, the stopcock and clamp are simultaneously 

 opened. The cover of the chamber is put on and the injection 

 allowed to proceed, all that is required being to maintain the 

 pressure in the apparatus as nearl}' constant as possible. 

 When the injection is complete, a clip is placed on the vena 

 cava, near its mouth, and the stopcock shut. [The special 

 methods to be used for the injection of particular organs, and 

 the methods of double injection, will be given under the proper 

 heads.] 



Injection with Solution of Nitrate of Silver. It is 

 preferable for this purpose to work with the apparatus, as it 

 is necessary to employ a considerable pressure. As soon as 

 the injection is completed, it must be replaced by water. This 

 is effected by substituting a flask containing water fo rthat 

 used for the nitrate of silver solution. The vessels must be 

 thoroughly streamed with water, otherwise the endothelial 

 markings are concealed by the quantity of precipitate which 

 is formed. 



Treatment of Injected Tissues. Organs injected with 

 colored masses must be suspended in ordinary alcohol in a 

 breaker. If a whole animal has been injected, the body must 

 be left to cool for half an hour or more. It must then be trans- 

 ferred to a large vessel containing common alcohol, to which 

 a few drops of glacial acetic acid have been added. It is a 

 good plan to transfer animals which have been injected with 

 gelatin masses to ice-cold alcohol, immediately after the com- 

 pletion of the injection; great care being taken in this, as in 

 every other case, to secure the artery and vein so as to avoid 

 all risk of escape of the mass. 



SECTION II. STRUCTURE OP THE BLOODVESSELS. 



Endothelium. The simplest method of demonstration is 

 to color the internal surface with silver. If the vessels are of 



