720 Plaster of Paris as an Injecting Mass. (November, 
tain consistency in order to have the resulting injection success- 
ful, therefore the amount of water could not be increased suffi- 
ciently to retard the setting over four or five minutes. As to the 
alum-plaster, it is difficult to obtain, and has the same objection 
as the mass to which size has been added; viz, it is. too long in 
setting, for it is often desirable to begin a dissection in compara- 
tive anatomy almost immediately after the injection has been 
made. 
It was noticed that a mass colored with carmine solution and 
afterwards acidulated with acetic acid remained fluid a much 
longer time than when colored with a red or blue with which no 
acid was used. Experiment showed that plaster mixed with an 
equal volume of ten per cent. acetic acid remained fluid ten to 
twenty minutes. The time was increased when carmine solution 
was used with the acid, as in practical injections, but not when 
any other colors were added. It was also found that if the plas- 
ter was mixed with either of the following solutions, instead of 
water, the setting was retarded ten to thirty minutes: A ten to 
twenty per cent. aqueous solution of alcohol or glycerine, or a ten 
per cent. solution of arseniate of soda. Either of these restrain- 
ers may be used with either of the colors. The arseniate and the 
acetic acid make the plaster friable, but the others do not. 
_ It is important to state that a mass which has been treated with 
a restrainer may be kept perfectly fluid much longer by agitation. 
This is also true of plaster and water, but not in so great a 
degree. 
In all of the experiments the plaster, after being thoroughly 
mixed with the fluid, was poured into small paper boxes like 
those used in imbedding for microscopical sections. It was found 
in practice that the plaster hardened much quicker in the blood 
vessels than in the paper boxes. This is probably because the 
restrainers and all superfluous liquid soak into the tissues, 
leaving only the amount of water necessary to eryelline the 
_ plaster. 
(5.) If one desires to make a permanent alcoholic or dried prep- 
| aration of any part or organ injected with plaster, the aniline 
colors must not be used, as they are not enduring. The alcohol 
should be seventy-five per cent. or stronger, and slightly acidu- 
lated with acetic acid (alcohol 200 parts, acid I part) to preserve 
te 9 of the oe blue and the carmine red (10, 202) 
ll 
