1878.) Plaster of Paris as an Injecting Mass. 719 
A thicker mass is much more difficult to manage. A slightly 
greater proportion of fluid may be used if the finest vessels are 
to be filled. The fluid includes all the liquid used in mixing the 
mass; viz, coloring liquids, restrainers and water. 
(3.) As to the red and blue colors, there are several that answer 
admirably. For red, vermilion or red lead ground in a mortar 
with a little water to get rid of lumps may be added in sufficient 
quantity to give a bright color. A saturated aqueous solution 
of magenta or red aniline is the easiest to use of all the red 
colors. It does not diffuse and color the tissues as one might 
expect, but colors the walls of the vessels a very bright red. An 
ammoniacal solution of carmine is, however, the best red. A 
sufficient quantity of this is added to the mass, and then the car- 
Mine is precipitated with fifty per cent. acetic acid. The acid 
should be poured into the colored mass, with constant stirring, 
till the color changes to the bright red of dry carmine, and there 
is a distinct odor of the acid. It is necessary to precipitate the 
carmine, as an alkaline solution diffuses through the walls of the 
vessels and stains the surrounding tissue. The advantage in pre- 
cipitating the carmine in the mass is its uniform diffusion. The 
same method is employed in coloring red the finest gelatin 
masses for histological injections (9, 10 and 11). 
A saturated solution of Berlin blue is the best blue, but as this 
is difficult to prepare (8, 403, 9, 164 and 10, 180), the ordinary ` 
Berlin or Prussian blue of the shops will answer if it is ground 
with water to a homogeneous paste. The simplest blue is, how- 
ever, a saturated aqueous solution of blue aniline. 
The aniline colors are the easiest to use, as it is simply neces- 
Sary to add to the mass a sufficient quantity of the solution to 
produce the desired tint. 
' (4.). It has been known a long time that if alum or borax is 
burned with gypsum, the resulting plaster will not set for three 
or four hours after mixing, but will finally set nearly as hard as 
marble (12). It is said by Tomlinson (13, I, 829) that ordinary 
plaster may be kept fluid four or five hours after mixing with 
water by adding a little sżze or beer; and it is a matter of common 
experience that the greater the proportion of water the longer it 
takes the plaster to set. It is necessary to give the mass a cer- 
'Leamon’s red and blue aniline dyes answer very well, and may be bought at any 
drug store, fe 
