I20 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 



oA of water or mercury is employed to force in the 

 I I I injection. This has the advantage of affording 

 r" r a steadier pressure then can be obtained in the 



1 ordinary manner. Fig. 37 represents this ap- 

 S paratus. Three bottles are required, each of 

 f 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 



I "^^ while the other merely passes 



f^^ •iM'-^ ^^ through the corks. One bottle 



.,r,;::: W— 1^ ^^^^^ (i) is filled with water and is 

 -■i — suspended by a string (a) pas- 



■ ''' sing over a pulley by which its 



height may be regulated. This bottle is connected with the 

 second (</) 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 



