OF MICROSCOPIC OBJECTS. 115 



CHAPTER VI. 



INJECTION. 



1. INJECTION is the filling of the arteries, veins, or other vessels 

 of animals with some coloured substance, in order that their natu- 

 ral arrangement may be made visible. This is, of course, a deli- 

 cate operation, and needs special apparatus, which I will now 

 attempt to describe. 



2. Syringe. This is usually made to contain about two ounces. 

 On each side of the part next to the handle is a ring, so that the 

 finger may be thrust through it, and the thumb may work the 

 piston as in an ordinary syringe. The plug of the piston must be 

 " packed " with wash-leather, and fit so closely as to be perfectly 

 air-tight ; and if, when it has been used awhile, it is found that 

 some of the liquid escapes past the plug into the back part of the 

 body, it must be repacked, which operation will be best under- 

 stood by examining the part These syringes are made of various 

 sizes, but in ordinary operations the above will be all that is 

 needed. The nozzle is about an inch long, and polished so accu- 

 rately that there is no escape when the pipes are tightly placed 

 upon it dry. 



3. The pipes are usually about an inch long, to the end of 

 which are affixed thicker tubes so as to fit the nozzle, as before 

 mentioned, whilst a short arm projects from each side of these? 

 so that the silk or thread which is used to tie the artery, &c., 

 upon the thin pipe may be carried round these arms, and all dan- 

 ger of slipping off prevented. The pipes are made of different 

 sizes, from that which will admit only a very fine needle (and 

 this will need now and then to be cleaned, or to be freed from 

 any chance obstruction), to that which will take a large pin. 

 These sizes must always be at hand, as the vessels of some sub- 

 jects are exceedingly minute. 



