TREY'S WHITE GELATIN MASS. 271 



the vessels much more distinct than the very pale mass of 

 Thiersch (No. 483). It is also easier to manage than 

 Thiersch's mass, as it does not solidify so quickly. It shows 

 well in the vessels by reflected, as well as by transmitted 

 light. 



485. Fol's Lead Chromate Gelatin Mass (Lehrb., p. 15). 



486. Hoyer's Silver Nitrate Yellow Gelatin Mass (Biol. Cen- 

 tralbl, ii, 1882, pp. 19, 22 ; Journ. Eoy. Mic. Soc. [N.S.], iii, 

 1883, p. 142). " A concentrated solution of gelatin is mixed 

 with an equal volume of a 4 per cent, solution of nitrate of 

 silver and warmed. To this is added a very small quantity 

 of an aqueous solution of pyrogallic acid, which reduces the 

 silver in a few seconds ; chloral and glycerin are added as 

 before" (see ante, HOYER'S formula for carmine-gelatin, 

 No. 472). 



This mass is yellow in the capillaries and brown in the 

 larger vessels. It does not change either in alcohol, chromic 

 or acetic acid, or bichromate of potash, &c. 



487. Hoyer's Green Gelatin Masses (ibid.}. Made by mixing 

 a blue mass and a yellow mass. 



488. Thiersch's Green Gelatin Mass (Arch.f. mik. Anat., 1865, 

 p. 149) . Made by mixing the blue mass, 479, and the yellow 

 mass, 483. 



489. Robin's Scheele's Green Gelatin Mass (see 464). 



490. Hartig's White Gelatin Mass (FEEY, Le Microscope, 

 p. 190). Dissolve 125 grammes of acetate of lead in so much 

 water that the whole shall weigh 500 grammes. 



Dissolve 95 grammes of carbonate of soda in so much 

 water that the whole shall weigh 500 grammes. 



Take equal volumes of the two solutions, and add two 

 volumes of gelatin solution. 



491. Frey's White Gelatin Mass (ibid.). Put into a tall glass 

 cylinder 125 to 185 grammes of cold saturated solution of 

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

 phuric 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- 



