FUNCTIONAL INERTIA AS LATENT PERIODS, &c. 23 



increasing. Fig. i shows tracing of the heart of a 

 rabbit beating in hot salt solution (NaCl) : it cannot be 

 induced to beat beyond about six times per second 

 as a maximum. 



The cells of the central nervous system have a 



FIG. i. Upper line: tracing of ventricle of heart of rabbit beating at 

 maximal rate in hot "normal saline" solution, six a second maxi- 

 mum. Lower line : half seconds. 



measurable and very distinct latent or refractory 

 period, demonstrated for cerebral cells by Richet,* 

 for those of the spinal cord by Horsley and Schafer.t 



Sir Victor Horsley J expressly points out, as impor- 

 tant in the diagnosis, the very long latent period in the 

 central nervous system after " shock." The symptoms 

 of traumatic neurasthenia may be so long in becoming 

 apparent, that certain clinicians have been led into 

 the error of asserting that the neurasthenia was 

 actually not caused by the so long antecedent injury. 



These refractory periods set the limits to the rate 

 of discharges from the central nervous system, 



* Richet, Nature, October 26, 1899. 



f Horsley and Schafer, Jouvn. Phys., vol. vii. p. 96. 



I Allbutt's " System of Medicine," vol. viii. p. 166. 



