022 VERTEBRATED ANIMALS. 



novices in the operation, and who are desirous of perfecting 

 themselves in the practice of the easier methods, before attempt- 

 ing the more costly. By M. Doyere, who first devised this 

 method, it was simply recommended to throw in saturated solu- 

 tions of the two salts, one after the other; but Dr. Goadby, who 

 has had much experience in the use of it, advises 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 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 suggest- 

 ing the substitution of nitrate for acetate of lead ; the resulting 

 nitrate of potash 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 em- 

 plo}^ed. For a ivhite 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 recom- 

 mended, 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 solutions of persulphate of 

 iron and ferrocyanide of potassium), which, to avoid the altera- 

 tion of its color by the free alkali of the blood, should be 

 triturated with its own weight of oxalic acid and a little 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. 



435. Injected preparations may be preserved either dry or in 

 fluid. The former method is well suited to sections of many 



solid organs, in which the disposi- 



n j\ FIG. 32 8. tion of the vessels does not sustain 



much alteration by drying ; for the 

 colors of the vessels are displayed 

 with greater brilliancy than by any 

 other method, when such slices, 

 after being well dried, are moist- 

 ened with turpentine and mounted 

 in Canada balsam. But for such 

 an injection as that shown in Fig. 

 328, in which the form and dispo- 

 sition of the intestinal villi would 

 be completely altered by drying, it 

 is indispensable that the prepara- 

 tion should be mounted in fluid, in 

 a cell deep enough to prevent any 

 pressure on its surface. Either Goadby's solution or weak spirit 

 answers the purpose very well. 



Villi of Small Intestine of Mo 



