CAFFEINE DIURKSIS '247 



When the muscle is exhausted then ligate the left thigh 

 tightly and drive a second carpet tack through the left 

 knee to hold the left gastrocnemius firmly. Isolate the 

 left tendo Achillis. Disconnect the stimulating wires, re- 

 move the frog hoard from the large clamp and turn the 

 frog board around on a perpendicular axis so that the frog 

 will be on the side away from the apparatus. Also remove 

 the large clamp, turn it over on a horizontal axis and re- 

 attach it to the stand. Replace the frog board. The left leg 

 of the frog will now occupy practically the same position 

 that the right leg formerly had. Attach the stimulating 

 wires and connect the tendon to the muscle lever. The 

 load, magnification, tension, etc., of this muscle must be 

 the same as that used with the right muscle. About twenty 

 minutes should now have elapsed for absorption of the 

 caffeine. 



Start at the beginning of the upper half of the drum 

 and record a fatigue curve of this muscle, which will now 

 show the effect which caffeine has on muscular work. The 

 rate of stimulation should not vary (once in one or two 

 seconds) for each curve. How does the normal fatigue 

 curve compare with the caffeine curve? What conclusions 

 can you draw? 



EXPERIMENT XL VIII. 

 Caffeine. (Rabbit: Diuresis, Cervical Nerves, Depressor.) 



1. Dissolve two grams of urethane in about twenty-five 

 cubic centimeters of water. Select a full grown rabbit 

 and with a catheter used as a stomach tube inject the 

 urethane into the rabbit's stomach. [Pass the tube 

 through the hole in a wood gag (Fig. 218) held in the 

 animal's mouth.] Wait about ten or fifteen minutes for 

 the drug to be absorbed and then give the animal a little 

 ether to bring on complete anesthesia. Use great care in 

 this for rabbits die very readily. Insert a tracheal can- 



