480 APPENDIX 



paper soaked in chloroform. Note the primary stimulating stage (in 

 which the animal struggles), with the acceleration and deepening of the 

 respirations, followed soon by the second stage, in which the respirations 

 become slower and shallower. The anesthetic should be removed at 

 this time lest the animal be killed by cardiac paralysis. Note the gradual 

 return to the normal respiration. 



In the remainder of the experiments frog-life may often be economized 

 greatly by arranging the order in which the experiments are performed 

 at each laboratory-period. The order matters little theoretically. 

 Experiments not requiring extensive cutting should be done before those 

 demanding it, therefore, and sometimes observations on the heart may 

 well be made the same day as experiments on the sartorius or gastroc- 

 nemius. 



VI. THE PHYSIOLOGY OF MUSCLE. 



Expt. 35. The nerve-muscle preparation is made out of the bipen- 

 niform gastrocnemius muscle, the whole sciatic nerve, and the femur of a 

 large frog. ' Quick and painless is the killing of the animal by disorganiz- 

 ing its brain and cord with a "seeker," which is thrust into the skull- 

 cavity through the foramen magnum by a single strong quick movement 

 at a point to be felt with the thumb-nail as a slight transverse depression 

 in the spinal column. Now with small scissors cut the skin circularly 

 around the lower part of the trunk, and seizing the skin on the back, 

 draw it off the legs with one pull. Cut the frog in two transversely and 

 then separate the legs, etc., by an incision with the scissors exactly in the 

 median line. Now dissect out the conspicuous sciatic nerve from the 

 knee through the thigh to the spinal cord, leaving attached to it a small 

 bit of the latter and the gastrocnemius muscle. Detach the tendo 

 Achillis from the bone and raise the gastrocnemius muscle with the for- 

 ceps by this tendon. Cut through the middle of the femur (to be used 

 as a handle), leaving it attached to the gastrocnemius. This is the 

 "nerve-muscle preparation" so much used in physiology. The removal 

 of both preparations complete from the frog should require not more 

 than five minutes after it has been done two or three times. The 

 preparation that is not to be used at once should be placed on the glass 

 plate and covered with filter-paper wet in modified Ringer's (Locke's) solu- 

 tion, the closest practicable approach to blood-plasma. The nerve should 

 be touched only by the glass rod, and never stretched nor allowed to 

 approach dryness. The muscle, too, should be handled as little as pos- 

 sible (especially with metallic implements) and kept wet. Every stimu- 

 lation of whatever sort of these now dying tissues shortens materially 

 their life and their experimental usefulness. 



The gastrocnemius muscles and the sciatic nerve are the most useful 

 for the purposes of these studies for several reasons. They are easily 

 and quickly dissected; the nerve is the longest and largest in the body; 

 the muscle is distinct; it is of the bipenniform type and thus very powerful; 



