i2O 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 

 (<) is filled with water and is 

 suspended by a string (a) pas- 



FlG. 37. ll 1 1 1 -x 



sing over a pulley by which its 



height may be regulated. This bottle is connected with the 

 second (d) by a rubber 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 



