272 INJECTIONS. 



precipitate is to be mixed with an equal part of concentrated 

 gelatin solution. 



Frey states that this is a very finely grained mass. Injected 

 organs may be preserved in chromic acid. 



492. Teichmann's White Gelatin Mass (ibid.,p. 191). "Take 

 3 parts of nitrate of silver dissolved in the gelatin solution, 

 and add 1 part of common salt." 



The mass is very fine-grained, and is not decomposed by 

 chromic acid; the disadvantage of it is that it blackens under 

 the influnce of light and of sulphurous solutions. 



493. Fol's Brown Gelatin Mass (Zeit. f. wiss. Zool., xxxviii, 

 1883, p. 494). 500 grms. of gelatin are soaked, and allowed 

 to swell up, in 2 litres of water in which 140 grms. of com- 

 mon salt have previously been dissolved ; the mass is melted 

 over a water-bath, and a solution of 300 grms. of nitrate of 

 silver in a litre of water is gradually added, with vigorous 

 shaking. (If it be desired to have an extremely fine-grained 

 mass, both the solutions should be diluted with 3 or 4 volumes 

 of water.) The mass is pressed out into strings as before 

 ( 473), and the strings are stirred up in clear daylight with 

 the following mixture : 1 \ litres of cold saturated solution 

 of potassic oxalate to 500 c.c. of cold saturated solution of 

 sulphate of iron. As soon as the whole mass is thoroughly 

 black the operation is at an end. The strings are then washed 

 for several hours, remelted, and poured on to the prepared 

 paper. 



494. Miller's Purple Silver Nitrate Gelatin Mass. See Amer. 

 Hon. Mic. Journ.j 1888, p. 50; Journ. Roy. Mic. Soc., 1888, p. 

 518; Zeit.f. wiss. Mik., v, 3, 1888, p. 361. 



495. Robin's Mahogany Gelatin Mass. See 461. 



496. Ranvier's Gelatin Mass for Impregnation (Traite, p. 123). 

 Concentrated solution of gelatin, 2, 3, or 4 parts ; 1 per 

 cent, nitrate of silver solution, 1 part. 



497. Fol's Metagelatin Vehicle (Lchrb., p. 17). The opera- 

 tion of injecting with the ordinary gelatin masses is greatly 

 complicated by the necessity of injecting them warm. FOL 

 proposes to employ metagelatin instead of gelatin. 



If a slight proportion of ammonia be added to a solution of 



