18 INTRODUCTION. 



origin in a formless matter ( Cytoblastema, germ-substance of cells) ; 

 what afterwards remains of this substance may be distinguished as 

 Intercellular substance (substantia inter cellular is). The cells are 

 vesicles, and consist of a fine membrane which encloses a fluid often 

 containing granules. For the most part these cells have a so-called 

 nucleus, a small dark-coloured corpuscle, lying on the wall of the 

 cell. In this nucleus a round spot has been distinguished and 

 termed nucleolus. The formation of these cells seems to proceed not 

 always in the same manner. According to SCHWANN a nucleolus 

 arises first, round this a nucleus is formed as its envelope, by the 

 aggregation of granules in the fluid germ-substance : at a slight 

 distance from this nucleus there coagulates, as it were, a thin mem- 

 brane, the Cell- wall, which at first is raised, like a watch-glass, on 

 one side of the nucleus, and afterwards encloses it all round. On 

 this account the nucleus is considered to be the germ of the cell 

 ( Cytoblastus] ; when the cell is formed, the nucleus, according to 

 SCHWANN, has discharged its office : it is detached and disappears. 

 The researches of HENLE T have shewn that such is not universally 

 the case, but that in fibrous tissues formed from cells, the cell- 

 nucleus is changed into peculiar fibres. 



Cells when once formed are multiplied by fission, or by the 

 formation of new cells within those already formed. The parts 

 then of those tissues, with which we have become acquainted 

 above, are either cells or fibres which have been formed from cells. 

 (1) In some tissues the cells, which have been plainly isolated, are 

 present as elements at a later period, as in adipose tissue and 

 cuticle ; (2) in other tissues the walls of the cells become thick- 

 ened, and coalesce with one another and with the intercellular sub- 

 stance, whilst the cavities remain separate, as in cartilage ; (3) in 

 others, again, the cavities coalesce, whilst the walls of the cells 

 that mutually touch, are destroyed or absorbed. Finally, other 

 tissues, still, exhibit as elementary parts little plates without 

 cavities, which may probably have existed at an earlier period. 

 These either join one another in a plane, or range themselves 

 lengthwise in a row, as in the fibres of organic muscles and of 

 Conjunctive Tissue. Other fibres may, according to HENLE, be con- 

 sidered as compound cells, i.e. those whose nucleus was originally 



1 HENLK, AUr/emrin? Anatomic, s. 188 9. 



