01 MICROSCOPIC OBJECTS. 175 



CHAPTER VII, 



INJECTION. 



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

 vessels of animals with some coloured substance, in order 

 that their natural arrangement may be made visible. This 

 is, of course, a delicate operation, and needs special appa- 

 ratus, 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 a 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 soft leather 

 well oiled or greased, in order to free it from all danger of 

 any liquid penetrating it, 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 understood 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 accurately that there is no escape 

 when the pipes are tightly placed upon it dry. 



3. The pipes are usually about an inch long, to their 

 ends are affixed thicker tubes so as to tit 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 upon the thin pipe, may be carried round these 

 arms, and all danger of slipping off prevented. The pipes 

 are made of different sizes, from that which will admit only 

 of a very fine needle (and this will need now and then to be 

 cleaned, or to be freed from any chance obstruction), to 



