THE NEURON 55 



The synapse, therefore, acts as a sort of valve, to use a crude 

 analogy, and appears to be one of the factors (not necessarily 

 the only one, see p. 97) in establishing the polarity of the neuron. 



5. Observations upon injured -neurons show that the degenera- 

 tions caused by the severance of their fibrous processes (whether 

 these be manifested as degeneration of the fibers or as chroma- 

 tolysis, see p. 49) or by the destruction of the cell bodies from 

 which the fibers arise cannot cross the barriers interposed by the 

 synapses. 



Summary. In this chapter the form and internal structure of 

 neurons have been briefly reviewed and the present status of the 

 neuron doctrine is summarized on p. 49. The synapse is. the 

 place where the nervous impulse is transmitted from one neuron 

 to another, and it is regarded as of the utmost physiological 

 importance, its most important features being presented briefly 

 on p. 54. The doctrine of the polarization of the neuron teaches 

 that nervous impulses are received by the dendritic processes 

 and transmitted outward from the cell body through the axon. 



LITERATURE 



APATHY, S. 1898. Ueber Neurofibrillen, Proc. Internal.- Zoological 

 Congress, Cambridge, pp. 125-141. 



BARKER, L. F. 1901. The Nervous System and Its Constituent Neurones, 

 New York. 



BETHE, A. 1904. Der -heutige Stand der Neurontheorie, Deutsch. 

 med. Woch., No. 33. 



. GOLGI, C. 1882-1885. Sulla fina anatomia degli organi centrali del 

 sistema nervoso, Riv. Sperim. di Freniatria, vols. viii, ix, and xi. 



. 1907. La dottrina del neurone, Teoria e fatti, Arch. Fisiol., vol. iv, 

 pp. 187-215. 



HEIDENHAIN, M. 1911. Plasma und Zelle, 2 Lieferung (in Bardelcben's 

 Handbuch der Anatomic des Menschen, Bd. 8), Jena. 



His, W. 1889. Die Neuroblasten und deren Entstehung im embry- 

 onalen Mark, Leipzig. 



MEYER, ADOLF. 1898. Critical Review of the Data and General Meth- 

 ods and Deductions of Modern Neurology, Jour. Comp. Neur., vol. viii, 

 pp. 113-148 and 249-313. 



NISSL, F. 1903. Die Neuronenlehre und ihre Anhanger, Jena. 



RAM6N Y CAJAL, S. 1909. Histologie de Systeme Nerveux, Paris. 



WALDEYER, W. 1891. Ueber einige neuere Forschungen im Gebiete 

 der Anatomic des Centralnervensystems, Deutsch. med. Woch., Bd. 17. 



