THE IDENTITY OF NEUROGLIA. 549 



structures should likewise present irregular swellings under 

 the influence of the same agencies, and that the axis-cylinder 

 should show less, the intracellular formation of plexuses and 

 anastomoses interposing a harrier to the too free passage of 

 plasma. That such is actually the case is illustrated by the 

 annexed plates by Berkley, which represent the lesions found 

 in the neurons of the poisoned animals to which reference has 

 been made. 



If the protoplasmic processes or dendrites are the first to 

 bear the brunt of the vascular engorgement, the plasma being 

 carried to them through fibrils connected with their tips, these 

 tips or extremities should first show evidence of the expansile 

 pressure. This is well illustrated in Fig. 1, a "psychical cell 

 from the second cellular layer of the cortex," which shows, using 

 Berkley's words, "a few pathological tumefactions on the upper- 

 most branches of the apices of the apical dendrite. Other- 

 wise the cell is normal/ 7 This cell was selected from a section 

 derived from the brain of an animal poisoned with ricin, death 

 having occurred in thirty-six hours. A feature of importance, 

 however, is that it is the main, or apical, dendrite that giving 

 off the greatest number of subdivisions which shows the evi- 

 dences of engorgement; the extremities of the other dendrites 

 are not thickened, but they show more or less marked evidences 

 of engorgement as the main trunk is approached. This ob- 

 viously suggests that the plasma penetrates the neuron by way 

 of the main dendrite and that it finds its way into its col- 

 laterals cellulipetally; in other words, that, instead of also 

 entering these collateral branches by way of their tips, it is 

 supplied to them by the main trunk precisely as if it were 

 the main stalk of a plant. Of course, this does not mean that 

 the apices of the collaterals may not subsequently show thick- 

 enings; being terminals, they should naturally do so when the 

 pressure exceeds a given limit. This feature is illustrated by 

 Fig. 2, especially by the larger stem of the main trunk. This 

 cell, a projection-cell from the second layer of the cortex, shows 

 the effects of forty-eight hours' ricin poisoning: i.e., of some- 

 what more prolonged engorgement. 



Worthy of special notice, also, is the fact emphasized by 

 Berkley (referring to Fig. 2), that: "there is now distinct 



