Februaey 15, 1918] 



SCIENCE 



155 



to extend in any particular way to the 

 structure that is most characteristic of the 

 cell body, namely, the nucleus. Struc- 

 turallj', therefore, there is no special rea- 

 son for assuming that the nucleus and its 

 surrounding cytoplasm constitute a special 

 nervous center. Moreover, as Bethe 

 (1S97, 1898) and Steinach (1899) have 

 shown, certain neurones may continue to 

 function for some considerable time after 

 the removal or destruction of their cell 

 bodies, thus demonstrating very clearly 

 that these bodies are not a necessary part 

 in the internal nervous mechanism of the 

 neurone. 



But not only can it be shown that the 

 cell body with its contained nucleus is not 

 essential to the nervous organization of the 

 neurone, it can also be shown that this 

 part has a very definite, specific and non- 

 nervous function of its own. It has come 

 to be an admitted fact in cytology that the 

 nucleus of a cell is in some very direct way 

 essential to the normal metabolism of that 

 element, for when a cell is cut into pieces 

 the non-nucleated fragments are incapable 

 of further growth and invariably die, 

 whereas the nucleated part may regenerate 

 and continue to live. To this rule the 

 nerve cell seems to be no exception, for 

 when a nerve fiber is separated from the 

 rest of the neurone, it invariably under- 

 goes degeneration and death. The nu- 

 cleated part meanwhile usually remains 

 intact, and is the part from which a new 

 nerve fiber will grow out if one is formed 

 at all. Thus the nucleated and non-nucle- 

 ated parts of the neurone act in the same 

 way as the corresponding parts of an ordi- 

 narj' cell do and hence it is concluded that 

 the nucleus of the neurone, like that of the 

 ordinary cell, is a structure essentially 

 concerned with metabolism. In this way 

 only is the nucleated part of the neurone 

 necessary to nervous processes. The older 



neurologists were certainly quite mistaken 

 when they regarded what they called the 

 ganglion cell as the center of nervous ac- 

 tivity. It is the metabolic or trophic cen- 

 ter of the neurone, but, though it may be 

 invaded by neurofibrils, it is not a seat of 

 special nervous function. Hence how mis- 

 leading and erroneous is it to discuss the 

 nervous polarity of the neurone as though 

 it centered on the cell body of that struc- 

 ture! 



The polarity of the neurone is best de- 

 scribed in the statement that nerve im- 

 pulses are received at one end of it and 

 discharged at the other. From this stand- 

 point polarity is not necessarily associated 

 with dendrites and neurites or with the cell 

 body, but depends upon the positional re- 

 lations of the neurone as a whole, espe- 

 cially in reference to the rest of the ani- 

 mal's body, including, in particular, other 

 neurones. If one end of a neurone forms 

 a part of a sensory surface, that end natu- 

 rally serves as the receptive end and the 

 opposite one becomes the region of dis- 

 charge. If the neurone is imbedded in 

 central nervous organs, its polarity is ap- 

 parently determined by the nature of the 

 synapses. Thus, though an impulse can 

 be transmitted in either direction within 

 the limits of a single neurone, it can pass 

 from one neurone to another only in one 

 direction. This principle is well illus- 

 trated by the Bell-Magendie law as ex- 

 tended by the observations of Gotch and 

 Horsley (1891), Mislawski (1895), Veszi 

 (1909) and others. When a stimulus is ap- 

 plied to the central end of the cut dorsal 

 root of a spinal nerve (Fig. 1), the ventral 

 root exhibits an electrical change and the 

 muscles connected with it contract show- 

 ing that a nerve impulse has passed 

 through the cord from the dorsal to the 

 ventral side. When on the other hand the 

 central end of a ventral root is stimulated, 



