The Theories of Cell Development. 
127 
as an intermediate stage of development. “ A cell was considered 
to be produced by the globules arranging themselves in a spherical 
form, so as to constitute a membrane, within which other globules 
remained, and formed contents.”* But they also believed that fibres 
were formed of elementary granules drawn up in a line. 
Concerning the so-called “ investment ” or “ cluster ” theory, 
which for a time was pretty generally accepted, Virchow says “the 
upholders of this theory imagined that originally a number of ele- 
mentary globules existed scattered through a fluid ; but that, under 
certain circumstances, they gathered together, not in the form of 
vesicular membranes, but so as to constitute a compact heap (mass, 
cluster , — Kliimpchen), and that this globe was the starting-point 
of all further development, — a membrane being formed outside and 
a nucleus inside by the differentiation of the mass by apposition or 
intussusception.”! This theory is a most singular conglomeration 
of truth and error : of truth, in that it concedes what we now know 
so well, namely, that the membrane is not a necessary part of the 
living cell ; of error, in that it practically recognizes free cell 
development. 
Probably the most strenuous and persistent advocate of the glo- 
bular (or, to adopt his own terminology, the molecular) theory at 
the present time is Professor Bennett, the eminent pathologist of 
Edinburgh. His theory is best given in his own words : — “ The ulti- 
mate parts of organization are not cells nor nuclei, but the minute 
molecules from which these are formed. They possess independent 
physical and vital properties, which enable them to unite and arrange 
themselves so as to produce higher forms. Among these are nuclei, 
cells, fibres, and membranes, all of which may be produced directly 
from molecules. The development and growth of organic tissues is 
owing to the successive formation of histogenetic and histolytic 
molecules. The breaking down of one substance is often the neces- 
sary step to the formation of another ; so that the histolytic or 
degenerative molecules of one period become the histogenetic or for- 
mative molecules of another.”! On the succeeding page he adds, 
“ As to development, the molecular is the basis of all tissues. 
The first step in the process of organic formation is the production 
of organic fluid ; the second, the precipitation in it of organic mole- 
cules, from which, according to the molecular law of growth, all 
other textures are derived either directly or indirectly,” — that is, 
with or without the intervention of cells. 
It will readily be seen that the theory of free cell development, 
as originally stated by Wolf and modified by Schleiden, and the 
globular or molecular theory, are, practically, one and the same 
* Virchow, ‘ Cellular Pathology,’ p. 53. 
X Bennett’s Lectures, p. 118. 
VOL. VIII. 
t Op. cit., p. 53. 
L 
