THE CIRCULATION OF CEREBRO-SPINAL SUBSTANCE. 579 



extremity of the main apical process or one of its collateral 

 branches, and not infrequently the extreme termination of the 

 dendron, is seen to be somewhat swollen when no other portion 

 of the cell is involved"** He also states that "in his description 

 of the mode of ending of the collaterals of the great pyramidal 

 cells" Cajal "describes their finest branches as terminating 

 freely by a nodosity" All these facts seem to us to warrant 

 the conclusion that each of the collateral dendrites of a neuron 

 and each axon, or subdivision of the latter, is supplied with a 

 bulbous end-organ. 



How is an axonal end-organ of one neuron functionally 

 related to that of a dendrite of another neuron? Berkley, 

 alluding to the subdivisions of the axon, each of which is sup- 

 plied with its bulbous end-organ, says: "These spherical ap- 

 paratuses are closely adjusted against the bulbous tips of the 

 gemmules, at times the approximation being so close that the 

 impression is given of actual contact, though it should be re- 

 membered that the slightest overlapping will produce the same 

 effect; and, on the whole, it is more probable that there is no 

 actual contact, but that the axonal discharges of the stimuli 

 overleap the infinitesimal distance between bulb and gem- 

 mule." For the reasons adduced, we do not think that the 

 gemmules serve for the reception of impulses. These reasons 

 also suggest that each axonal end-organ can only discharge its 

 stream of impulses into the bulbous terminal of a neighboring 

 dendrite, which bulbous terminal would, under these circum- 

 stances, present some analogy with the end-bulb of Krause, 

 and, indeed, with several peripheral sensory organs. We have 

 also submitted reasons that seem to us to offset the assertion 

 that the end-organs actually touch. Indeed, that an "infin- 

 itesimal distance" between the efferent axonal end-organ and 

 the afferent dendritic end-organ exists seems to be the only con- 

 clusion warranted by the histological picture, as described by 

 Berkley. It seems to us, in other words, that each of the bulbous 

 end-organs of an axon, though apparently in contact with the end- 

 organ of one of the dendrites of a neighboring neuron, may be 

 separated from it by an infinitesimal distance. 



w All italics are our own. 



37 



