ADDRESS. 19 



though, as Gardiner contends, the connecting threads would be the medium 

 for the conduction of impulses and of food from a cell to those which lie 

 around it. For the plant cell therefore, as has long been accepted in the 

 animal cell, the wall is reduced to a secondary position, and the active con- 

 stituent is the nucleated cell plasm. It is not unlikely that the absence of a 

 controlling nervous system in plants requires the plasm of adjoinino- cells 

 to be brought into more immediate contact and continuity than is the 

 case with the generality of animal cells, so as to provide a mechanism for 

 harmonising the nutritive and other functional processes in the different 

 areas in the body of the plant. In this particular, it is of interest to note 

 that the epithelial tissues in animals, where somewhat similar connectin"' 

 arrangements occur, are only indirectly associated with the nervous and 

 vascular systems, so that, as in plants, the cells may require, for nutritive 

 and other purposes, to act and react directly on each other. 



Nerve, Cells, 



Of recent years great attention has been paid to the intimate struc- 

 ture of nerve cells, and to the appearance which they present when in 

 the exercise of their functional activity. A nerve cell is not a secretin"- 

 cell ; that is, it does not derive from the blood or surrounding fluid a 

 pabulum which it elaborates into a visible, palpable secretion charac- 

 teristic of the organ of which the cell is a constituent element, to be in 

 due course discharged into a duct which conveys the secretion out of 

 the gland. Nerve cells, through the metabolic changes which take place 

 in them in connection with their nutrition, are associated with the pro- 

 duction of the form of energy termed nerve energy, specially exhibited 

 by animals which possess a nervous system. It has long been known 

 that every nerve cell has a body in which a relatively laro-e nucleus is 

 situated. A most important discovery was the recognition that the body 

 of every nerve cell had one or more processes growing out from it. More 

 recently it has been proved, chiefly through the researches of Schultze 

 His, Golgi, and Ramon y Cajal, that at least one of the processes the 

 axon of the nerve cell, is continued into the axial cylinder of a nerve 

 fibre, and that in the multipolar nerve cell the other processes or 

 dendrites, branch and ramify for some distance away from the bodv. A 

 nerve fibre is therefore an essential part of the cell with which it is 

 continuous, and the cell, its processes, the nerve fibre and the collaterals 

 which arise from the nerve fibre collectively form a neuron or structural 

 nerve unit (Waldeyer). The nucleated body of the nerve cell is the 

 physiological centre of the unit. 



The cell plasm occupies both the body of the nerve cell and its pro- 

 cesses. The intimate stfucture of the plasm has, by improved methods 

 of observation introduced during the last eight years by Nissl and con- 

 ducted on similar lines by other investigators, become more definitely 

 understood. It has been ascertained that it possesses two distinct * 



c2 



