1878. | Plaster of Paris as an Injecting Mass. 721 
The part to be preserved should not be placed in alcohol till the 
plaster has become thoroughly hardened. An hour will usually 
suffice. 
Practical Application of the Plaster Mass—It will be readily 
seen that the plaster mass is far superior to a wax mass for ordi- 
nary work. It is simply necessary to mix it well with an equal vol- 
ume of fluid; and the subject needs only to be bled. Wax involves 
great expense and trouble in preparation, and both it and the 
subject must be thoroughly warmed before the injection can be 
made (7, II, 100 and 3). The warming is objectionable especially 
with cold blooded animals.} 
Plaster is also very neat, it never softens, but makes the injected 
vessels like cylinders of stone. It penetrates very finely, filling 
arteries half a millimeter in diameter, and has a great range of uses. 
It is well adapted to fill various ducts, like the thoracic, pancreatic, 
etc. The valves in the veins, the semilunar valves of the aorta 
and pulmonary artery may be most satisfactorily demonstrated 
with it, and with a little care and experience the action of the 
auriculo-ventricular valves of the heart may be nicely shown. 
Vessels or ducts injected with plaster may be dissected out 
neatly, and placed on cardboard to dry. The appearance of the 
dried preparation is nearly like that of the fresh specimen, as the 
plaster prevents shrinkage. Preparations so made will last indefi- 
nitely if they are well poisoned with arseniate of soda before dry- 
ing. Specimens injected with plaster colored with Berlin blue and 
carmine, have kept three months in slightly acid alcohol without 
the least change. 
The accompanying diagrams are introduced to show the cheap- 
ness and simplicity of an injecting apparatus, and its practical 
application in plaster injecting. 
n 8-ounce lead or britannia syringe, with a leather packed 
piston, works very well indeed and costs less than one dollar. 
The canula is so large, Fig. II, 1, that it cannot be put into the 
vessels. Fine canule for this purpose a be made by any per- 
lIt is objectionable to warm thoroughly a mammalian animal after death, as it 
greatly hastens decomposition. It is particularly objectionable to warm cold-blooded 
animals, for the warm water, into which they must be put, acts as a powerful stimu- 
= causing general tetanus, unless one waits half a day or a day after apparent _ 
eath. The tissues, especially of amphibians, are greatly softened by the warm . 
water, in fact partially cooked. It is also a great deal of trouble to warm the ani- 
mal and the mass in summer. 
