740 INJECTED PREPARATIONS. 



accessible elsewhere to such as desire to put it iu practice.* 

 Injections may be either Opaque or Transparent, each method 

 having its special advantages. The former is most suitable where 

 solid form and inequalities of surf ace are specially to be displayed, 

 as in Figs. 394 and 400 ; the latter is preferable where the injected 

 tissue is so thin as to be transparent (as in the case of the Retina 

 and other membranes of the Eye), or where the distribution of its 

 blood-vessels and their relations to other parts may be displayed 

 by Sections thin enough to be made transparent by mounting either 

 in Canada balsam or in Glycerine medium (Plate xxv.). — The 

 Injection is usually thrown into the vessels by means of a Brass 

 Syringe expressly constructed for the purpose, which has several 

 jet-pipes of different sizes, adapted to the different dimensions of 

 the vessels to be injected ; and these should either be furnished 

 with a stopcock to prevent the return of the injection when the 

 syringe is withdrawn, or a set of small corks of different sizes 

 should be kept in readiness, with which they may be plugged. 

 The pipe should be inserted into the cut end of the trunk which is 

 to be injected, and should be tied therein by a silk thread. In 

 injecting the vessels of Fish, Mollusks, &c, the softness of the 

 vessels renders them liable to break in the attempt to tie them ; 

 and it is therefore better for the operator to satisfy himself with 

 introducing a pipe as large as he can insert, and with passing it 

 into the vessel as far as he can without violence. All the vessels 

 from which the injection might escape should be tied, and some- 

 times it is better to put a ligature round a part of the organ or 

 tissue itself; thus, for example, when a portion of the Intestinal 

 tube is to be injected through its branch of the Mesenteric artery, 

 not only should ligatures be put round any divided vessels of the 

 mesentery, but the cut ends of the intestinal tube should be firmly 

 tied. — For making those minute Injections, however, which are 

 needed for the purposes of Anatomical investigation, rather than to 

 furnish 'Preparations' to be looked-at, the Author has found the 

 Glass-Syringe (Fig. 83), so frequently alluded-to, the most efficient 

 instrument ; since the Microscopist can himself draw its point to 

 the utmost fineness that will admit of the passage of the injection, 

 and can push this point without ligature, under the Simple Micro- 

 scope, into the narrowest orifice, or into the substance of the part 

 into which the injection is to be thrown. — Save in the cases in 

 which the operation has to be practised on living animals, it should 

 either be performed when the body or organ is as fresh as possible, 

 or after the expiry of sufficient time to allow the rigor mortis to 



* See especially the article 'Injection,' in the " Micrographic Dic- 

 t onary;" M. Robin's work, " Du Microscope et des Injections" (Paris, 

 1849) ; Prof. II. Frey'a Treatise " Das Mikroskop und die Mikroskopische 

 Technik," 2nd Edition (1865) ; and Dr. Beale's "How to Work with the 

 Microscope," 4th Edition (II 



