130 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



process through which an impulse is sent out from the cell to 

 reach another neuron or a cell of some other tissue. The neuron, 

 so far as conduction is concerned, shows a definite polarity, 

 the conduction in the dendrites being cellulipetal, in the axons, 

 cellulifugal. 



The neuron doctrine, so far as the name at least is concerned, dates from 

 a general paper by Waldeyer,* in which the newer work up to that time was 

 summarized. The main facts upon which the conception rests were furnished 

 by His (1886), to whom we owe the generally accepted belief that the nerve 

 fiber (axis cylinder) is an outgrowth from the cell, and secondly by Golgi, 

 Cajal, and a host of other workers, who, by means of the new method of Golgi, 

 demonstrated the wealth of branches of the nerve cells, particularly of the 

 dendrites, and the mode of connection of one nerve unit with another. The 

 view that these units are anatomically independent and on the embryological 



Fig. 59. Motor cell, anterior horn of gray matter of cord. From human fetus (Lenho8~ 

 sek): * marks the axon; the other branches are dendrites. 



side are derived each from a single epiblastic cell (neuroblast) has proved 

 acceptable and most helpful; but the validity of this hypothesis has been 

 called into question from time to time. As was stated on p. 127, Bethe has 

 claimed that in young animals the nuclei of the neurilemmal sheath may 

 regenerate a new nerve fiber containing axis cylinder and myelin sheath, and 

 this fact, if true, at once brings into question the hitherto accepted belief 



* " Deut. med. Wochenschrift," 1891, p. 50. 



