620 VERTEBRATED ANIMALS. 



for themselves. For this reason, no more than a general account 

 of the process will be here offered ; the minute details which need 

 to be attended to, in order to attain successful results, being 

 readily accessible elsewhere to such as desire to put it in practice. 1 

 The coloring matter which is altogether most suitable when only 

 one set of vessels is to be injected, is Chinese vermilion. This, 

 however, as commonly sold, contains numerous particles of far 

 too large a size ; and it is necessary first to reduce it to a greater 

 fineness by continued trituration in a mortar (an agate or a steel 

 mortar is the best) with a small quantity of water, and then to 

 get rid of the larger particles by a process of "levigation," ex- 

 actly corresponding to that by which the particles of coarse sand, 

 &c., are separated from the Diatomacese (p. 305). The fine 

 powder thus obtained, ought not, when examined under a mag- 

 nifying power of 200 diameters, to exhibit particles of any appre- 

 ciable dimensions. The " size" or "gelatine" should be of a fine 

 and pure quality, and should be of suificient strength to form a 

 tolerably firm jelly when cold, whilst quite limpid when warm. 

 It should be strained, whilst hot, through a piece of new flannel; 

 and great care should be taken to preserve it free from dust, 

 which may best be done by putting it into clean jars, covering 

 its surface with a thin layer of alcohol. The proportion of levi- 

 gated vermilion to be mixed with it for injection, is about 2 oz. 

 to a pint; and this is to be stirred in the melted size, until the 

 two are thoroughly incorporated, after which the mixture should 

 be strained through muslin. The injection is 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 stop cock 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 return of the injection when the syringe is withdrawn, or a set 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 offish, 

 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 sometimes 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. The 

 operation should either be performed when the body or organ is 



1 See especially the article "Injection." in the " Micro^raphic Dictionary ;" Dr. Beale's 

 treatise on "The Microscope, and its application to Clinical Medicine," Chap, viii; and 

 M. Robin's work, " Du Microscope et des Injections." (Paris, 1 849.) (See also Appendix.) 



