124 The Theories of Cell Development. 
tenia ), granules are first seen, “ some of which increase in size and 
assume the form of a minute vesicle, the nucleus of the future cell. 
On the addition of water to this, granules become apparent in its 
interior, and one of these, larger than the rest, appears to be the 
nucleolus. Around the nucleus, as is generally stated, the cell mem- 
brane is developed, and thus the cell is completed.” * Virchow’s 
account of Schleiden’s theory does not exactly agree in terms with 
the one quoted above, although the practical difference amounts to 
nothing ; it is as follows : f — “ According to the view which 
was put forward in the first instance by Schleiden, and accepted 
by Schwann, the connection between the three coexistent cell 
constituents was long thought to be on this wise, — that the 
nucleolus was the first to show itself in the development of tissues 
by separating out of a formative fluid (blastema, cytoblastema), 
that it quickly attained a certain size, that then fine granules were 
precipitated out of the blastema and settled around it, and that 
about these then condensed a membrane. That in this way a 
nucleus was completed, about which new matter gradually gathered, 
and in due time produced a little membrane (the celebrated c watch- 
glass ’ form).” In the one case, granules are first produced, and, 
by their aggregation, the nuclei are afterwards formed ; in the 
other, the nuclei take the precedence, the granules being a secondary 
product. Seeing that the nucleus was discovered several years 
previously (1833) by Brown, of Edinburgh, and that Schleiden 
had conferred upon it the name of “ cytoblast ” or “ cell-bud,” thus 
directly implying his belief in its importance in relation to cell 
growth, it is more than probable that Virchow’s account is the 
more correct one. Schwann, whose observations seem to have been 
confined chiefly to animal structures, adopted the views of Schleiden 
concerning the development of vegetable cells, and applied them to 
the genesis of the cells of animals. He “ was of opinion that the 
extracellular formation of cells — that is, their development in free 
blastema — was the most frequent mode of their production in 
animals.” f At this period, therefore, the theory of free or spon- 
taneous cell development was generally accepted by histologists ; 
and, seeing that Schleiden and Schwann gave to this notion the 
support of their great authority, it is by no means a matter of 
surprise that it found general favour. 
Passing by the more recent advocates of spontaneous cell- 
growth, especially Bennett, of Edinburgh, Carpenter, and Todd and 
Bowman, § with the remark that they are simply recasts of the 
* Peaslee’s ‘Human Histology,’ p. 120. f ‘Cellular Pathology,’ p. 35. 
X Strieker’s ‘ Histology,’ vol. i., p. 34. 
§ ‘The Physiological Anatomy and Physiology of Man,’ edition of 1857. It 
is proper to observe that in the last edition (1866), now issuing in parts under the 
editorship of Dr. Lionel Beale, the well-known cell theory of the latter is presented. 
