548 S. WALTER RANSON 



It is possible, of course, that these complex formations in the 

 sjMnal ganglion may furnish points of contact for the transmission 

 of ner\'ous impulses between afferent neurones or even between 

 afferent and sympathetic neurones. But there is no physiological 

 evidence that such an interchange of hnpulses does occur in the 

 spinal ganglion. Furthennore, these branches, bulbs, and 

 plexuses seem to be arranged in a manner unfavorable for the 

 occurrence of points of contact between neurones. Only in a few 

 cases, as where the end bulb on the branch of one cells lies under 

 the capsule of another cell, has the possibility of such contact 

 been demonstrated. 



It must also be remem.bered that these multiple processes, 

 bulbs, and plexuses vary greatly in their development in different 

 animals. In the dog the simple unipolar type represents the vast 

 majority of the cells, while in man the m.ore complex form.s pre- 

 dominate. In view of this great variation in their development, 

 it is clear that whatever function these accessory structures 

 may have, it can not be of a fundamental character. 



It was at f rst supposed by Cajal and others that it would be 

 possible to classify the spinal ganglion cells into functionally 

 separate and distinct groups according to these variations in their 

 external form. This position is still maintained by some, but 

 it is becoming evident that it is untenable. Two reasons for 

 abandoning this position have already been presented; namely, 

 the apparent ineffectiveness of these processes for transmitting 

 nerve impulses, and the great variation in their development 

 in closely related groups of animals. 



The third reason for abandoning the conception that these alter- 

 ations from the simple type represent the outward characteristics 

 of fixed and functionally distinct groups of spinal ganglion cells 

 is found in observations on pathological and transplanted spinal 

 ganglia. These observations show that the form of a given 

 spinal ganglion cell is not fixed, that it may undergo rapid changes, 

 and that under proper stimulation cells of the simple unipolar 

 type may be transformed into complcA cells shnilar to those seen 

 in normal ganglia. Such observations have been made by a 

 number of observers. 



