IS REPORT — 1900. 



secretion is colourless, and the comparison of their appearance when 

 secretion is going on with that seen when the cells are at rest, have 

 shown that the cell plasm is much more granular and opaque, and con- 

 tains larger particles, during activity than when the cell is passive ; the 

 body of the cell swells out from an increase in the contents of its plasm, and 

 chemical changes accompany the act of seci'etion. Ample evidence, there- 

 fore, is at hand to support the position taken by John Goodsir, nearly 

 sixty years ago, that secretions are formed within cells, and lie in that 

 part of the cell which we now say consists of the cell plasm ; that each 

 secreting cell is endowed with its own peculiar property, according to the 

 organ in which it is situated, so that bile is formed by the cells in the 

 liver, milk by those in the mamma, and so on. 



Intimately associated with the process of secretion is that of nutri- 

 tion. As the cell plasm lies at the periphery of a cell, and as it is, alike 

 in secretion and nutrition, brought into closest relation with the sur- 

 rounding medium, from which the pabulum is derived, it is necessarily 

 associated with nutritive activity. Its position enables it to absorb 

 nutritive material directly from without, and in the process of growth it 

 increases in amount by interstitial changes and additions throughout its 

 substance, and not by mere accretions on its surface. 



Hitherto I have spoken of a cell as a unit, independent of its 

 neighbours as regards its nutrition and the other functions which it has 

 to discharge. The question has, however, been discussed, whether in a 

 tissue composed of cells closely packed together cell plasm may not give 

 origin to processes or thi-eads which are in contact or continuous with 

 corresponding processes of adjoining cells, and that cells may therefore, to 

 some extent, lose their individuality in the colony of which they are 

 members. Appearances were recognised between 1863 and 1870 by 

 Schron and others in the deeper cells of the epidermis and of some 

 mucous membranes which gave sanction to this view, and it seems possible, 

 through contact or continuity of threads connecting a cell with its neigh- 

 bours, that cells may exercise a direct influence on each other. 



Nageli, the botanist, as the foundation of a mechanico-physiological 

 theory of descent, considered that in plants a network of cell plasm, 

 named by him idio-plasm, extended throughout the whole of the plant, 

 forming its specific molecular constitution, a)id 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 

 lie conceived to be built up of a nucleated cytoplasmic network, each 

 nucleus with the branching cell plasm surrounding it being a centre of 

 activity. On this view a cell would retain to some extent its individuality. 



