246 



EXPERIMENTAL PHARMACOLOGY 



available then a student can interrupt tlie primary cur- 

 rent with a simple key by hand (once in one or two sec- 

 onds). The drum must have a slow speed. The second- 

 ary shocks are carried directly to the muscle by very fine 

 copper wires one of which is attached to the carpet tack 

 which is driven through the frog's right knee into the frog- 

 board to hold the upper end of the gastrocnemms muscle 

 firmly in place when the muscle contracts. The other wire 

 is tied to the tendo Achillis. Now inject into the dorsal 

 lymph sac one cubic centimeter of five -tenths per cent caf- 



Rubber tube 

 - w/re 



I 



Cannula with points for cats* rabbits 



Point for doqs 



Fig. 225. A method for making cannulas with separable points. One end of the 

 "T" of a glass (5/16 inch) T-tube is cut off short and short glass points are attached 

 liy means of a piece of rubber tubing. It is vastly easier to make the small points than 

 to blow a T-tube and to make a cannula entirely of glass. (The points illustrated are 

 larger than they should be for rabbits and cats. ) 



feine solution (Greene) and allow this to be absorbed 

 while the experiment is going on. 



When all adjustments are made start the drum and 

 record a normal ''fatigue curve'! from the right gastroc- 

 nemius. (For a description of fatigue curves see any 

 manual on experimental physiology.) This curve should 

 be taken on the lower half of the drum. 



