110 VASCULAR SYSTEM. 



CHAPTER VII. 



VASCULAR SYSTEM. 



SECTION I. METHODS OP INJECTION. 



BEFORE describing the structure of the bloodvessels and 

 lymphatics, an account will be given of the methods of inject- 

 ing. The processes of injection may be divided according as 

 they are used during life or after death. 



Methods of Injecting during Life. The method of 

 injecting the vessels of an animal during life has, hitherto, not 

 been much employed. It may be practised either for the pur- 

 pose merely of introducing into the circulation any suitable 

 liquid containing coloring matters, or other substances in 

 solution or suspension, or ^"ith a view to emptying the vessels 

 of their contents and substituting another liquid. For ex- 

 ample, we have already seen that insoluble coloring matters 

 are introduced in order to feed the colorless blood corpuscles 

 and those of the connective tissue ; and we shall subsequently 

 see that by the injection of colored solutions, a "natural 

 injection," produced by excretion of the ducts of certain 

 glandular organs, may be obtained. (See Chapter X.) The 

 most important insoluble coloring matters are vermilion, car- 

 mine, and anilin, which are used suspended in salt solution, as 

 described in Chapter 1. p. 26. Insoluble Prussian blue, as 

 precipitated by the gradual addition of alcohol to the solution, 

 can also be used iiv the same way. 



The methods are as follow : 



Injection of the Frog during Life. In a large frog, 

 secured on its back, the abdominal vein is carefully exposed 

 under a dissecting lens, in its course up the middle line of the 

 anterior wall of the belly. A ligature is passed round the 

 distal end of the prepared part and tightened. A small clip 

 is then placed on the proximal end, and a ligature passed 

 under the vein between the two, which is looped, but not 

 tightened. The vein having then been opened just beyond the 

 loop, with a pair of sharp scissors, a fine glass canula is 

 introduced in the direction of the circulation. The loop is 

 then tightened round the canula and knotted. The canula 

 must now be filled, with the aid of a capillary pipette, with, 

 salt solution, and connected by a bit of india-rubber tubing 

 with a brass syringe, in doing which great care must be taken 



