OF MICROSCOPIC OBJECTS. 181 
and there tied; so that all danger of accidentally with- 
drawing the pipe is obviated. Care must now be used im 
closing ali the vessels which communicate with that where 
the pipe is placed lest the injecting fluid escape; and this 
must be done by tying them with silk. Should, however, 
any of these be left open by accident, the bulldog forceps 
must be used, as before recommended. 
18. The part to be injected must now be immersed in 
warm water, not, however, above 100° Fahrenheit, and left 
until the whole is thoroughly warmed. Whilst this is being 
done, the coloured size must be made ready by the pot being. 
placed in the tin bath of warm water, which must be of 
sufficient temperature (about 110° Fahrenheit) to keep it 
perfectly liquid.. For the same purpose, the syringe is often 
tightly covered with two or three folds of flannel; and; 
indeed, there is no part of the process which requires more 
attention. If the substance to be injected is too hot, it is 
injured; whilst, if any of the articles are too cold, the gela- 
tine, or size, loses a part of its fluidity, and consequently 
cannot enter the minute vessels. When all is prepared, the 
syringe, with the stopcock attached, should be warmed, and 
then filled and emptied with the injecting fluid two or three 
times, care being taken that the end of the syringe be kept 
beneath any bubbles which form upon the surface. The 
syringe may then be filled, and closely attached to the pipe 
which is tied in the vessel. With a firm and steady pressure 
the piston must be forced downwards, when the substance 
will be perceived to swell, and the colour show itself in places 
where the covering is thin. When the syringe is almost 
emptied of its contents, the stopcock must be turned to pre- 
vent any escape of the injection from the subject. It must 
then be refilled, as in the first instance, and the process 
repeated. I say almost emptied, because it is well not to 
force the piston of the syringe quite to the bottom, lest the 
small quantity of air which frequently remains be driven 
into some of the vessels, and the object be injured or quite 
ruined. As the injection is continued, it will be found that 
