STIMULATION AND TRANSMISSION 287 



(Qio = i.3).^ For the irritable tissues of the frog, Lucas^ 

 gives the following determinations (at ca. 13°): sub- 

 stance/3 (nerve end-plate) of the sartorius, .001 second; 

 motor nerve- trunk, .003 second; muscle fiber (sartorius), 

 .02 second; ventricle, 2 seconds; for smooth muscle the 

 period is much longer (several seconds) . Lapicque finds 

 the least effective duration of the minimal stimulating 

 current to vary widely for the muscles of different 

 animals, and gives the following data:^ 



Tv«-,„^i„ Least Effective Duration 



^"^^^^ of Threshold Current 



Gastrocnemius (rana esculenta) 003 sec. 



Gastrocnemius (r. temporaria) 007 sec. 



Rectus abdominis (r. esculenta) 009 sec. 



Gastrocnemius (bufo vulgaris) 013 sec. 



Foot of snail (helix pomatia) 048 sec. 



Foot of snail (solen marginatus) 075 sec. 



Ventricle of tortoise (testudo grasca) 082 sec. 



Claw muscle of crab (carcinus moenas) 30 sec. 



Mantle muscle of mollusc (aplysia punctata) . . .80 sec. 



These determinations illustrate the specificity of this 

 time-factor for different animals. It is interesting to 

 note that the velocities of the motor nerve impulses in 

 different animals vary in a closely parallel manner. 

 To designate this characteristic time-factor in the 

 electrical stimulation of different irritable systems, 

 Lapicque has introduced the term ''chronaxie." As 

 now defined, the term has reference to the least duration 

 required by a current of exactly twice the threshold 

 intensity (or so-called "rheobase"). 



^ Lucas and Mines, Journal of Physiology, XXXVI (1907), 334; 

 Lucas, ihid., XXXIX (1910), 461; of. p. 472. 



2 Lucas, Journal of Physiology, XL (1910), 225; of. p. 245. 



3 Lapicque, Compt. rend. soc. bioL, LVII (1905), 503. 



