VERTEBRATED ANIMALS. 295 



after the other; but Dr. G-oadby, who had much experience in the use of 

 it, advised that gelatine should be employed in the proportion of 2 oz. 

 dissolved in 8 oz. of water, to 8 oz. of the saturated solutions of each 

 salt. This method answers very well for the preparations that are to be 

 mounted dry; but for such as are to be preserved in fluid, it is subject 

 to the disadvantage of retaining in the vessels the solution of acetate of 

 potash, which exerts a gradual corrosive action upon them. Dr. Goadby 

 has met this objection, however, by suggesting the substitution of ni- 

 trate for acetate of lead; the resulting nitrate of potasli having rather a 

 preservative than a corrosive action on the vessels. When it is desired 

 to inject two or more sets of vessels (as the arteries, veins, and gland- 

 ducts) of the same preparation, different coloring substances should be 

 employed. For a whit* injection, the carbonate of lead (prepared by 

 mixing solutions of acetate of lead and carbonate of soda, and pouring- 

 off the supernatant liquid when the precipitate has fallen) is the best 

 material. No blue injections can be much recommended, as they do 

 not reflect light well, so that the vessels filled with them seem almost 

 black; the best is freshly precipitated 

 prussian blue (formed by mixing solu- FIG. 479. 



tions of persulphate of iron and ferro- 

 cyanide of potassium), which, to avoid 

 the alteration of its color by the free 

 alkali of the blood, should be triturated 

 with its own weight of oxalic acid and 

 a litte water, and the mixture should 

 then be combined with size, in the pro- 

 portion of 146 grains of the former to 4 

 oz. of the latter. 



689. Opaque injections may be pre- 

 served either dry or in fluid. The former 

 method is well suited to sections of many 

 solid organs, in which the disposition of 

 the vessels does not sustain much alte- 

 ration by drying; for the colors of the ves- 

 sels are displayed with greater brilliancy 



than by any other method, when such slices, after being well dried, are mois- 

 tened with turpentine and mounted in Canada balsam. But for such an 

 injection as that shown in Fig. 479, in which the form and disposition 

 of the intestinal villi would be completely altered by drying, it is indis- 

 pensable that the preparation should be mounted in fluid, in a cell deep 

 enough to prevent any pressure on its surface. Either G-oadby's solution 

 or weak Spirit answers the purpose very well; or by careful manage- 

 ment even such may be mounted in Canada balsam or Dammar. 



690. Within the last few years, the art of making transparent Injec- 

 tion has been much cultivated, especially in Germany; and beautiful 

 preparations of this description have been sent over from that country 

 in large numbers. The coloring-matter is chiefly employed is Carmine, 

 which is dissolved in liquid ammonia; the solution (after careful filtra- 

 tion) being added in the requisite amount to liquid gelatine. 



The following is given by Dr. Carter as a formula for a carmine injection 

 which will run freely through the most minute capillaries, and which will not 

 tint the tissues beyond the vessels themselves, a point of much importance: Dis- 

 solve 60 grains of pure carmine in 120 grains of strong liquor ammoniee (Pharm. 

 Brit.), and filter if necessary; with this mix thoroughly l oz. of a hot solution 



