36 GENERAL ANATOMY OF THE TISSUES. 



quently grow with their cells, (nerve-cells, ova) ; but except 

 when dividing they never assume any but the globular form. 



Schwann has given an explanation of the 

 F ' s *2!' ^^ growth, as well of the ceil as of the nucleus. 

 He considers that the molecules of the 

 cell-membrane exert an attractive influence 

 upon the fluid which surrounds them, and 

 deposit its newly-formed particles among 

 themselves ; if the deposition take place 

 between the molecules already present in 

 the substance of the membrane, the cell 

 becomes distended; if it take place only in the direction 

 of the radius of the cell, the membrane becomes thickened. 

 The nucleus grows less than the cell, because as soon as the 

 latter is formed it no longer comes into direct contact with the 

 concentrated cytoblastema. General growth takes place when 

 the molecules of the membranes all attract equally ; partial 

 growth, when this happens only or especially at particular spots, 

 where the apposition of new matter takes place to a greater 

 extent. With reference to the mode of formation of precipi- 

 tates and of crystals, this theory appears to me to explain very 

 well the phenomena of general growth, supposing that we 

 ascribe to the cell-membrane the faculty of readily taking up 

 molecules and applying them to its increase. Such, however," 

 must be the case, for the relations of the nuclei, which even 

 when free, never grow very considerably, and particularly never 

 in one direction? show that the power of growth is not simply 

 innate in every organic membrane, manifesting itself when 

 sufficient formative material is offered, but requires peculiar 

 conditions which are realised only in the cell-membrane. To 

 account for partial growth, Schwann's view must be somewhat 

 extended ; for only those modes of growth in which the cells, 

 during their increase in certain directions, lose nothing of 

 their original dimensions in others, can be interpreted in 



Fig. 11. Six developing bone-cells from a rickety bone as yet sharply defined from 

 the interstitial substance : — a, simple bone-cells ; b, a compound one, answering to 

 a parent cell with two secondary cells ; c, similar ones with three cells, x 350. 



1 [This is surely incorrect. The " nuclei" in the hair-pulp, in the tooth-pulp, in 

 connective tissue, in organic muscle, grow in one direction to a very considerable 

 extent. — Eds.] 



