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plication of cell-structure, which being always absent in the 

 healthy gland-cell and almost all other animal cells, cannot 

 fairly be regarded as a part of the histological unit. But the 

 discussion of this superadded structure, and its histological 

 homology, must be reserved until we have entered in greater 

 detail into cell-physiology. 



The term cell is here used as a technicality for that 

 elementary part or histological unit, which consists o{ nucleus 

 and plasm ; the nucleus being always distinguishable by those 

 chemical or physical properties first shown by Dr. Beale to be 

 possessed by it in common with the germinal matter of the 

 ovum. 



Formerly the term nucleus was used very vaguely, size being 

 generally the only diagnostic character. Thus we find even 

 Virchow continually speaking of cells, when correctly (as we 

 now know by the nuclear test) he ought to say nuclei. 



When we examine the tissues of the embryo, we find them 

 crowded with nuclei, which have grown from the germinal 

 matter of the ovum, and if this examination takes place when 

 the parts differ from one another in form rather than texture, 

 we find an aggregation of nuclei separated only by a small 

 quantity of interposed plasm. The mass may be broken down 

 into what have been called cells, but there is no true speciali- 

 sation into these structures ; the nuclei bring away the sur- 

 rounding plasm only in the same way that the stones in a wall 

 that has been thrown down bring away adhering mortar. 

 Soon, however, in the tissues that are to become simply cellu- 

 lar the embryonic plasm is, for a given distance around the 

 nucleus, so acted upon — perhaps by insterstitial addition — 

 that a small portion is localised. This localised unit of 

 nucleated plasm is the typical cell, as we find it throughout 

 its active life in the gland. But in many epidermal structures, 

 though best in the caecal extremities of certain glands among 

 the lower animals, we find this same process of cell-formation 

 going on through life. Glancing at such a structure in the 

 deepest layer, we again see the nuclei crowded together, at 

 first hardly separated, but as we ascend, gradually getting 

 more and more spaced by intervening plasm, which as 

 gradually alters in texture until Ave have specialised histo- 

 logical units. And after the cell, has arrived at maturity, as 

 surely as the relative proportion of the nucleus to the plasm 

 diminishes, so surely does the working jjower of the cell 

 decrease. 



Now, having completed the anatomical life-history of the 

 cell, it becomes necessary to consider its function, secretion. 

 Formerly this process was regarded merely as separation. 



