442 BIOLOGICAL PHYSICS 



this machinery of life in the vegetable and lower animal 

 worlds, and in all its vital operations, we do not once see 

 the necessity for the existence of any other nervous 

 system, nor does that necessity arise until the conditions 

 of life and environment so change that, more or less, 

 " struggle for existence " on the part of the individual 

 animal or community of animals, takes place, when the 

 necessity for locomotion ensuing a supplementary and 

 additional nervous system makes itself felt, and compels 

 the formation, or evolution, of what is called a systemic 

 nervous system^ and the " introduction into the physio- 

 logical management of affairs " of the principle of a dual 

 control. 



The material mechanism, or fibre-cellular texture, com- 

 posing the sympathetic nervous system is, as we have 

 elsewhere contended, made up of every living cell and 

 connecting fibre engaged in the vital, or organic, work 

 of the bodily textures, as distinguished from merely 

 mechanical work, which is often effected through the 

 instrumentality of textures which have ceased to perform 

 actual vital work, but which are still continuous with the 

 textures so engaged, and used by them as supports, points 

 of attachment, protection media, and auxiliary agencies 

 generally. The sympathetic nerve textures, therefore, thus 

 comprehend every cell, with the fibrous processes uniting 

 that cell to its neighbouring cell, and the connexus of 

 such cells and fibrous processes throughout the organically 

 active whole, and thus necessarily constitute all living 

 textures, with one exception, viz. the systemic nerve 

 textures proper, composing the systemic nervous system, 

 which are made up of neurons or nerve units, each 

 of which is composed of cell protoplasm, nucleus, and 

 nucleolus enclosed in a cell wall, continuous from the 

 dendritic processes of the cell to the outer neurilemmar 

 environment of the nerve terminals this cell wall and 

 its axonal continuation, moreover, being a sympathetic 

 nervous system product. 



These statements involve and seem to justify the further 

 statement, that there are but two vital formative and life- 

 sustaining organisms within the individual animal body 

 on which the whole phenomena composing its living, 



