C. CIRCULATION. 



XVII. The circulation and its ultimate cause, a. To 



observe the capillary circulation, b. To observe 



the action of the frog's heart. 



a. To observe the capillary circulation. 



1. Appliances. Cork board 3 cm. wide by 20 cm. long and 

 about y?, cm. thick; cover glasses, 18 mm. in diameter 

 and 10 mm. in diameter; normal salt solution; camel's 

 hair brush ; pins ; compound microscope; sealing wax ; 

 thread ; filter paper ; 2 per cent croton oil in olive oil. 



2. Preparation. 



Pith two frogs the day before the observation is to be 

 made. At the beginning of the laboratory period when 

 the observation is to be made curarize the frog lightly by 

 the hypodermic injection of one drop of a 1 per cent 

 solution of curare. Make a frog-board by cutting a hole 

 1.5 cm. in diameter near one corner of the cork board 

 and fasten a large cover glass over the hole with sealing 

 wax. 



j. Operation. After the frog becomes curarized, pin it out 

 ventral surface downward in such a way as to bring one 

 of the hind feet over the hole in the board. Tie thread, 

 not too tightly, to the third and fourth digits, loop the 

 threads over pins and gently separate the digits until the 

 web is quite flat and closely approximated to the surface 



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