324 



PHYSIOLOGY 



CHAP. 



of the skin has been removed, according to Moinmsen. There 

 must, therefore, be other paths of excitation besides the cutaneous 

 nerves, probably from the sensory nerve-endings in the muscles 

 and tendons. 



Since the spinal tone that governs muscular tone is reflex, 

 not automatic, it may be asked whether it depends exclusively 

 upon the afferent excitations and is a constant quantity, or can 



FIG. 186. Tracings of homulateral reflexes of hind-limb of marsh tortoise, obtained with uniform 

 and rhythmically recurrent stimuli. (Fano.) To avoid confusion between the separate reflexes 

 by (superposition of the curves, a special mechanical contrivance was fitted by which the 

 writing-point was removed from the drum at a given moment after stimulation. The points of 

 stimulation are marked below the series of curves, and the time in ^}, n sec. The vertical 

 lines that coincide with each stimulation were ruled with a T square to show the reaction-time. 

 Tracings reduced by J. 



vary automatically, independent of any extrinsic influence, in 

 consequence of periodic oscillations or variations in the excitability 

 and metabolism of the central organ ? 



Fano (1903) from a systematic study of the reflex movements 

 of the marsh tortoise (Umi/s palustris) adduced experimental 

 evidence for the last view. He invented an apparatus by which 

 the animal could be excited at regular intervals by faradic break 

 shocks of constant strength, the reflex reactions being recorded at 

 regular distances on a smoked drum. He proved that the motor 

 reactions are not uniformly vigorous, but exhibit continuous 



