THE GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM 105 



activity is found to be greatly increased during the transmission 

 of a nervous impulse ; and nervous conduction evidently involves 

 a chemical change in the conducting fiber. The rate of trans- 

 mission of a nervous impulse depends on the structure and 

 physiological state of the nerve-fiber involved. The metabolic 

 activity of the nerve-cells is of a very different sort from that of 

 nerve-fibers, and may be characterized as of the explosive type. 

 There are at least two factors involved in the fatigue of the 

 nervous system: (1) fatigue of excitation, resulting from the 

 consumption of the materials of its protoplasm, and (2) fatigue 

 of depression, resulting from the accumulation of toxic products 

 of cellular activity. Each of these processes produces its own 

 very special series of morphological changes in the neurons. 

 The neurological functions involved in sleep and the higher 

 mental processes are as yet unknown. 



LITERATURE 



BUCHANAN, FLORENCE. 1908. On the Time Taken in Transmission of 

 Reflex Impulses in the Spinal Cord of the Frog, Quart. Jour. Exp. Physiol., 

 vol. i, pp. 1-66. 



CHILD, C. M. 1914. Susceptibility Gradients in Animals, Science, N. S., 

 vol. xxxix, No. 993, pp. 73-76. 



DOLLEY, D. H. 1911. Studies on the Recuperation of Nerve-cells After 

 Functional Activity from Youth to Senility, Jour. Med. Research, vol. xxiv, 

 pp. 309-343. 



. 1914. On a Law of Species Identity of the Nucleus-plasma Norm 

 for Nerve-cell Bodies of Corresponding Types, Jour. Comp. Neur., vol. 

 xxiv, pp. 445-501. 



. 1914. Fatigue of Excitation and Fatigue of Depression, Intern. 

 Monatsschrift f. Anat. u. Physiol., Bd. 31, pp. 35-62. 



DONALDSON, H. H. 1899. The Growth of the Brain, New York, chapters 

 xiv to xvii. 



HODGE, C. F. 1892. A Microscopical Study of Changes Due to Func- 

 tional Activity in Nerve-cells, Jour. Morphology, vol. vii, pp. 95-168. 



LADD, G. T., and WOODWORTH, R. S. 1911. Elements of Physiological 

 Psychology, New York. 



STILES, P. G. 1914. The Nervous System and Its Conservation, Phila- 

 delphia. 



TASHIRO, S. 1913. Carbon Dioxide Production from Nerve-fibers when 

 Resting and when Stimulated; a Contribution to the Chemical Basis of 

 Irritability, Amer. Jour, of Physiol., vol. xxxii, pp. 107-136. 



TASHIRO, S., and ADAMS, H. S. 1914. Carbon Dioxide Production from 

 the Nerve-fiber in a Hydrogen Atmosphere, Amer. Jour, of Physiol., vol. 

 xxxiv, pp. 405-413. 



. 1914. Comparison of the Carbon Dioxide Output of Nerve- 

 fibers and Ganglia in Limulus, Jour, of Biological Chemistry, vol. xviii, 

 pp. 329-334. 



