OF MICROSCOPIC OBJECTS. 181 



and there tied; so that all danger of accidentally with- 

 drawing the pipe is obviated. Care must now be used in 

 closing all 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 beicg 

 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 



