September 14, 1900.] 



SCIENCE. 



387 



gave sanction to this view, and it seems 

 possible through contact or continuity of 

 threads connecting a cell with its neigh- 

 bors, that cells may exercise a direct influ- 

 ence on each other. 



ISTageli, the botanist, as the foundation 

 of a mechanico-physiological theory of de- 

 scent, considered that in plants a net- 

 work of cell plasm, named by him idio- 

 plasm, extended throughout the whole of 

 the plant, forming its specific molecular 

 constitution, and that growth and activity 

 were regulated by its conditions of tension 

 and movements (1884). 



The study of the structure of plants with 

 special reference to the presence of an 

 intercellular network has for some years 

 been pursued by Walter Gardiner (1882- 

 97), who has demonstrated threads of cell 

 plasm protruding through the walls of 

 vegetable cells and continuous with similar 

 threads from adjoining cells. Structurally, 

 therefore, a plant may be conceived to be 

 built up of a nucleated cytoplasmic net- 

 work, each nucleus with the branching cell 

 plasm surrounding it being a center of 

 activity. On this view a cell would retain 

 to some extent its individuality, 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 sec- 

 ondary position, and the active constituent 

 is the nucleated cell plasm. It is not un- 

 likely that the absence of a controlling 

 nervous system in plants requires the plasm 

 of adjoining 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 harmon- 

 izing 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 con- 

 necting arrangements occur, are only in- 

 directly 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. 



NEEVE CELLS. 



Of recent years great attention has been 

 paid to the intimate structure of nerve 

 cells, and to the appearance which they 

 present when in the exercise of their func- 

 tional activity. A nerve cell is not a se- 

 creting cell ; that is, it does not derive 

 from the blood or surrounding fluid a pabu- 

 lum which it elaborates into a visible, palpa- 

 ble secretion characteristic 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 con- 

 nection with their nutrition, are associated 

 with the production of the form of energy 

 specially exhibited by animals which pos- 

 sess a nervous system, termed nerve energy. 

 It has long been known that every nerve 

 cell has a body in which a relatively large 

 nucleus is situated. A most important dis- 

 covery was the recognition that the body 

 of every nerve cell had one or more proc- 

 esses growing out from it. More recently 

 it has been proved, chiefly through the re- 

 searches of Schultze, His, Golgi, and Eamon 

 y Cajal, that at least one of the processes, 

 the axon of the nerve cell, is continued into 

 the axial cylinder of a nerve fiber, and that 

 in the multipolar nerve cell the other proc- 

 esses, or dendrites, branch and ramify for 

 some distance away from the body. A nerve 

 fiber is therefore an essential part of the 

 cell with which it is continuous, and the 

 cell, its processes, the nerve fiber and the 

 collaterals which arise from the nerve fiber 

 collectively form a neuron or structural 

 nerve unit (Waldeyer). The nucleated 



