18 



INTRODUCTION 



in the muscle. Placing the fresh-cut end of the nerve in a saturated 

 solution of common salt brings about a series of contractions in the 

 muscle. The muscle also contracts when the nerve is stimulated with 



a weak electric cur- 

 rent. If the nerve 

 muscle preparation 

 be placed on a copper 

 plate, and the tem- 

 perature of the latter 

 be raised above or 

 lowered below the 

 normal, there will oc- 

 cur variations in the 

 response of the mus- 

 cle to stimuli. (Elec- 

 trical stimulation will 

 be found most con- 

 venient.) The rela- 

 tion of muscular 

 action to temperature 

 will thus be striking- 

 ly represented. These 

 experiments with the 

 nerve-muscle prepa- 

 ration show that the 

 living substance is 

 irritable, unstable, and 

 conductive of stimuli. 



M. biceps. sm M. semimembranosus. 5 ' Cells. The 



M. gastrocnemius. st M. semitendinosus. amoeba and the white 



M. pyriformis. ta M. tibialis anticus. blood corpuscles al- 



ready studied furnish 

 very good examples 

 of cells which have no fixed form nor definite shapes. The red blood 

 corpuscles of the frog are cells in which the nucleus can be easily dis- 

 cerned by aid of the microscope (Fig. 4, p. 16). 



Fig. 7. 



Muscles of the left leg of the frog. Fig. 8 shows 

 distribution of the sciatic nerve. 



ad M. adductor magnus. sc sciatic nerve. 



b 



y 



p 



pe M. peroneus. tr M. triceps. 



H M. rectus interims minor. 



