120 NATURALISTS’ ASSISTANT. 
INJECTING. 
The circulatory system is best studied in injected speci- 
mens. ‘These are prepared as follows: an artery or other 
vessel is exposed and opened and in the opening the nozzle 
of the injecting apparatus is inserted. Usually an injecting 
syringe is use. ‘This is a metal instrument, closely resembling 
the ordinary “surgeon’s syringe,” provided with 
nozzles of various sizes. Sometimes instead of a 
syringe an apparatus is used in which the weight 
of water or mercury is employed to force in the 
injection. This has the advantage of affording 
a steadier pressure then can be obtained in the 
ordinary manner. Fig. 37 represents this ap- 
paratus. Three bottles are required, each of 
which is corked with a stopper through which 
two glass tubes pass. One of each pair of tubes 
goes to the bottom of the bottle 
while the other merely passes 
through the corks. One bottle 
(4) is filled with water and is 
suspended by a string (@) pas- 
FIG. 37. 
sing over a pulley by which its 
height may be regulated. ‘This bottle is connected with the 
second (@) by arubber pipe attached to the long glass tube 
in each. This in turn is connected with the third by a second 
rubber pipe attached to the short glass tube and from this 
bottle runs a rubber pipe bearing the glass injecting nozzle. 
The methods of use are as follows: the tube connecting 
