VERTEBRATED ANIMALS. 297 



of gelatine (1 to 6 of water); mix another oz. of the gelatine solution with 

 86 minims of glacial acetic acid; and drop this, little by little, into the solution of 

 carmine, stirring briskly the whole time. After the part has been injected, and 

 lias been hardened either by partial drying or by immersion in the Chromic acid 

 solution or in Alcohol, thin sections are cut with a sharp razor; and these are usu- 

 ally dried and mounted in Canada balsam. 



Many of these transparent injections '(Plate xxv.) are peculiarly well 

 seen under the Binocular Microscope, which shows the capillary net- 

 work not only in two dimensions (length and breadth), but also in its 

 third dimension, that of its thickness; this is especially interesting in 

 such injections as that (fig. 1) of the villi of the Intestine (seen in situ 

 in a transverse section of its tube), a thin section of the Mouse's toe 

 (fig. 2), or the convoluted layer of the Brain (fig. 3). The Stereoscopic 

 effect is best seen, if the light reflected through the object be moderated 

 by a ground-glass, or even by a piece of tissue-paper, placed behind it. 

 This method, however, does not serve to display anything well, save 

 the distribution of the Capillary vessels; the structures they traverse 

 being imperfectly shown. For the purpose of scientific research, there- 

 fore, the method followed by Dr. Beale (for full details of which the 

 reader is referred to his Treatise) is much to be preferred. 



The material recommended by him for the finest injections is prepared as fol- 

 lows: Mix 10 drops of the tincture of perchloride of iron (Pharm. Brit.) with 1 

 oz. of glycerine: and mix 3 grains of ferrocyanide of potassium, previously dis- 

 solved in a little water, with another 1 oz. of glycerine. Add the first solution 

 very gradually to the second, shaking them well together; and lastly, add 1 oz. 

 of water, and 3 drops of strong hydrochloric acid. This ' prussian "blue fluid,' 

 though not a solution, deposits very little sediment by keeping; and it appears 

 like a solution even when examined under high magnifying powers, in conse- 

 quence of the minuteness of the particles of the coloring matter. Where a second 

 color is required, a carmine injection may be used, which is to be prepared as 

 follows: Mix 5 grains of carmine with a few drops of water, and, when they are 

 well incorporated, add about 5 drops of strong liquor ammonise. To this dark-red 

 solution add about oz. of glycerine, shaking the bottle so as to mix the two 

 fluids thoroughly ; and then very gradually pour in another oz. of glycerine acidu- 

 lated with 8 or 10 drops of acetic or hydrochloric acid, frequently shaking the 

 bottle. Test the mixture with blue litmus paper; and mix with it another - oz. 

 of glycerine, to which a few drops more acid should be added, if the acid reaction 

 of the liquid should not have previously been decided. Finally, add gradually 2 

 drachms of alcohol previously well mixed with 6 drachms of water, and incor- 

 porate the whole by thorough shaking after the addition of each successive 

 portion. 



The staining process ( 202) may be combined with the injecting; but Dr. 

 Beale has now come to prefer the following method, when such a combination is 

 desired. An alkaline carmine fluid rather stronger than that ordinarily employed 

 (carmine 15 grs., strong liq. ammonias drachm, glycerine 2 oz., alcohol 6 

 drachms) is first to be injected carefully with very slight pressure; the ammonia 

 having a tendency to soften the walls of the vessels. When they are fully dis- 

 tended, the preparation is to be left for from 12 to 24 hours, in order that time may 

 be allowed for the carmine liquid which has permeated the capillaries, to soak 

 through the different tissues and stain the germinal matter fully. Next a little 

 pure glycerine is to be injected, to get rid of the carmine liquid; and the prussian 

 blue fluid is then to be injected with the utmost care. When the vessels have 

 been fully distended, the injected preparation is to be divided into very small pieces; 

 and these are to be soaked for an hour or two in a mixture of 2 parts of glycerine 

 and 1 of water, and then for three or four days in strong glycerine acidulated with 

 acetic acid (5 drops to 1 oz.). Preparations thus made are best mounted in Gly- 

 cerine jelly; and may then be examined with the highest powers of the Micro- 

 scope. 



A well-injected preparation should have -its vessels completely filled 

 through every part; the particles of the coloring matter should be so 



