16 



PRACTICAL PHYSIOLOGY 



to the nerve, and the sciatic nerve is freed from the surrounding tissues 

 as far as the knee. The thigh is then severed from the body by a 



FIG. 22. FIG. 23. 



Diagrams of a muscle- and nerve-preparation. (Pembrey and Phillips.) 

 FIG. 22. The first stage of dissection. 



FIG. 23. The second stage of dissection. The sciatic nerve exposed and the gastroc- 

 neniius muscle covered by skin. 



transverse cut close to the articulation of the head of the femur (Figs. 



22 and 23). 



In order that the best results may be obtained the muscle- and 



nerve-preparation should be as 

 fresh and irritable as possible, 

 and in order to obtain this the 

 following precautions should 

 be observed, (a) All apparatus 

 for the experiment should be 

 in working order before the 

 dissection is commenced, (b) 

 The muscle must be prevented 

 from drying by keeping the 

 "trouser" of skin pulled down 

 over it, and since the nerve 

 is even more easily killed by 

 drying, it should, when not 

 required for immediate stimu- 

 lation, be allowed to lie among 

 the muscles of the thigh, the 



FIG. 24. The crank-lever, muscle-board and stand. fo 



lymph of which will keep it 

 moist and irritable. The nerve must not be placed upon the frog's 



