52 Tue Microscope, 
is complete. All vessels communicating with the one connected 
with the pipe must now be tied with silk. Some vessels that 
have escaped notice will be discovered as soon as the injecting 
mixture commences to flow. The “bull-nose forceps” will 
catch them up firmly. Turn the stop-cock now and remove the 
body of the syringe. Be sure that the syringe is in proper 
order and that it fills well with the mixture. Just before bring- 
ing the syringe in contact with the pipe it is best to force out a 
drop or two in order to get rid of all the air. Fit it tightly now 
to the pipe in the preparation, turn the stop cock, and with a 
firm pressure empty the syringe of about three-fourths of its 
contents, again refill and inject until the operation is complete. 
The pipe containing the stop-cock should be left on the pipe 
that is inserted in the preparation. Nothing but experience will 
enable one to tell when the operation is complete. The beginner 
will be quite liable to cease operations too soon rather than too 
late. 
INJECTING MIXTURES. 
Blood vessels are best filled with a fluid which becomes 
solid in ordinary temperatures. Gelatine forms the foundation 
of such mixtures, for it can be liquified at blood heat and it 
solidifies at a little lower temperature. It is easily cut and 
coloring matter mixes readily with it. When gelatine masses 
are used, of course they must be kept hot while in use and the 
preparations to be injected must likewise be kept warm, gen- 
erally by placing them in hot water. However, if a recently 
killed animal is to be injected, the heat of the body itself will 
be found sufficient to keep the hot injecting mass in a fluid 
state. After using these mixtures the preparation is placed in 
cold water long enough to allow the gelatine to set when it is 
divided into parts as required, and placed in equal parts of wa- 
ter and alcohol or other hardening media. 
SEILER’S CARMINE GELATINE. 
This is a very desirable injecting mass. It is best to pur- 
chase it of dealers in microscopical accessories, as it is difficult 
to prepare. It sells for one dollar an ounce, and an ounce of the 
gelatine is dissolved in ten ounces of water. : 
