INJECTION. 



[ 423 ] 



INJECTION. 



for it is difficult of description. Tlie plug 

 must work air-tight in the tube, which may 

 be proved by depressing the handle as far as 

 possible, then closing the nozzle of the sy- 

 ringe with one finger, withdrawing the 

 handle to its fullest extent, and letting it 

 go, when it should fly entirely home. If 

 this does not take place, the plug must be 

 re-leathered. 



The handle of the syringe should be 

 graduated ; i. e. transverse lines should be 

 scratched upon it with the end of a file, or 

 in some other way, so that when its de- 

 scending movement is so slow as not to be 

 felt by the hand, it may be indicated to the 

 eye. 



The syi'inges, and in fact all the mechani- 

 cal apparatus requisite for injection, may be 

 purchased of Mr. Neeves, Regent Square, or 

 of Mr. Ferguson, Smithfield. 



The syringe must accurately fit the stop- 

 cocks and pipes. 



Injectitig-pipes. — These must be of various 

 sizes, to suit those of the vessels into which 

 they are to be introduced; they are furnished 

 with two short transverse arms, by which 

 they may be tied to the vessel. The smallest 

 pipes which are made, easily become stopped 

 up unless thoroughly cleansed after use ; to 

 remove any obstruction.a very fine " broach"- 

 needle made of watch-spring is required, 

 and may be procured of Mr. Ferguson as 

 above. 



Stopcocks. — One or two of these are use- 

 ful in stopping the injection from returning, 

 when the sjiinge is removed, or force ceases 

 to be applied to it. 



Forceps. — One or two pairs of small tena- 

 culum forceps must be at hand ; these are 

 noticed in the Ixteoduction, p. xxv. 



Jars or other vessels for holding the in- 

 jection. These may consist of confectioners' 

 jam-pots, or may be made of tin. The 

 former have the advantage of retaining the 

 heat for a considerable time. When in use, 

 the jars must be placed in a water-bath, or 

 in a tin vessel containing water, and placed 

 over a stove. 



Stirring-rods. — These must be made of 

 wood. 



Size. — The colouring-matters used for 

 the coarser injections are mostly insoluble 

 powders. These are usually mixed with 

 size or some form of solution of gelatine, 

 which holds them in suspension better than 

 water. 



The size mostly used is Yoimg's patent 

 size, and it is sold in the shops. It should 



be clear and fresh. Those who cannot 

 obtain this may prepare its equivalent by 

 dissolving 1 part of glue in 8 or 10 parts 

 of water with the aid of heat. 



The principal liquid injections used may 

 be arranged according to their colours. In 

 regard to the proportions of the colouring- 

 matter to that of the size, it must be re- 

 marked that these vary as used by different 

 injectors; and that, in general, when the 

 vessels to be injected are very minute, and 

 the objects are to be viewed by transmitted 

 light, the size should be thinner, and the 

 proportion of pigment less, than under the 

 opposite conditions. When the injection 

 is directed to be strained, this must be done 

 through a piece of new flannel wrung out 

 of hot water, or through a "tammy sieve," 

 which is more convenient. In preparing 

 the injections, great care must be taken 

 that the jars are perfectly clean, and that 

 no old injection remains adherent to them. 

 The colouring-matters, whether dry or dis- 

 solved, should be added to the size previ- 

 ously warmed in the water- bath, or the tin 

 vessel mentioned above ; and the whole 

 should be stirred until thoroughly incorpo- 

 rated. When trituration is spoken of, it 

 must be understood that the rubbing in a 

 mortar should be continued for a long time, 

 until the substance is reduced to the finest 

 possible state of powder. 



Harting recommends pi'eparing a stronger 

 size than that mentioned above, containing 

 1 part of glue to 4 of water, and that the 

 chemical substances be dissolved in the 

 additional water requisite before being 

 added to the size, which would seem to be 

 preferable ; but we have found the method 

 recommended to answer every purpose, and 

 it has the advantage of greater simplicity. 



Med Injection. — This is best made with 

 vermilion (bisulphuret of mercury), which 

 before use should be carefully examined as 

 to its purity from minute colourless crys- 

 talline particles, by viewing it by reflected 

 light, when they are easily detected. When 

 the vessels to be injected are very minute, 

 the vermilion is best previously levigated, 

 i. e. ti'itm'ated in a mortar with a small 

 quantity of water, the whole beino' after- 

 wards thrown into a large amount ot water, 

 and allowed to settle for a few seconds, so 

 that the coarser particles still left may sub- 

 side ; the upper portions of the liquid, con- 

 taining the tiner parts of the powder, are 

 then poured off and allowed to settle, the 

 supernatant water being again poured off, 



