SriNAL COED AND NERVES 



325 



irregularly periodic oscillations. The curves of Fig. 186 represent 

 this phenomenon. The time marking, obtained from a tuning 

 fork of 100 vibrations per second, and the exact moment of 

 stimulation, are recorded below the muscle tracings. By measur- 

 ing the distance between the single stimuli and the corresponding 

 reactions, the latent period of the latter is arrived at. Another 

 interesting fact then comes out, that besides the irregular periodic 

 oscillations in the amplitude of the reactions, there are similar 

 oscillations in the reaction time. 



Fano's experiments demonstrate that the automatic variations 

 of special excitability above described, which give a character of 

 irregular oscillating periodicity to the spinal tone in the tortoise, 



FIG. 187. Tracing a.s in last figure, after cervical transection of the cord. (Fano.) 



depend on influences coming from the brain, particularly from 

 the medulla oblongata. These periodic oscillations diminish when 

 by removing the fore-brain the inhibitory influence of the mid- 

 brain is unchecked. If the optic lobes are also destroyed, so that 

 the automatic activity of the bulb is given free rein, the oscilla- 

 tions once more become very conspicuous and far exceed those 

 observed under normal conditions. After dividing the thoracic 

 cord they diminish considerably in the hind-limbs ; after cervical 

 transection they decrease in the fore-limbs (Fig. 187). 



Fano's observations give further confirmation of the inhibitory 

 influence of the optic lobes already referred to (p. 319), and of the 

 automatic activity of the spinal bulb, to be discussed in the next 

 chapter. These automatic oscillations of the excitability of the 

 cord are merely the spread, almost one might say the reflection, of 

 those more marked waves that occur in the bulb, the existence of 



