230 INJECTIONS. 



chlorate of baryta. Add drop by drop, very carefully, 

 sulphuric acid. Allow the precipitate that forms to settle for 

 twelve hours, then decant almost all the clear supernatant 

 liquid. The remaining mucilaginous mass containing the 

 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. 



465. 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 influence of light and of sulphurous solutions. 



466. FoPs Brown Gelatin Mass (Z&it. f. wiss. Zool., xxxviii, 

 1883, p. 494). Five hundred grammes of gelatin are soaked, 

 and allowed to swell up, in two litres of water in which 140 

 grammes of common salt have previously been dissolved ; 

 the mass is melted over a water-bath, and a solution of 300 

 grammes 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 three or four volumes of water.) The mass is 

 pressed out into strings as before ( 446), 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, re- 

 melted, and poured on to the prepared paper. 



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

 Mon. Mic. Journ., 1888, p. 50; Jouni. Roy. Mic. Soc., 1888, 

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



468. Robin's Mahogany Gelatin Mass (see 435). 



469. 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. 



470. Fol's Metagelatin Vehicle (Lehrb., p. 17). The opera- 



