THE ORGANIC CELL 
25 
the cells of certain plants, which on section do give the appear- 
ance of a honeycombed structure. These cells being separated 
by distinct solid walls, Schwann (the father of the cell-theory) 
mistook these solid walls for their essential physiological part. 
The living portion filling up the spaces was at first probably 
mistaken for a waste product. H. von Mohl, in 1846, named 
this living substance protoplasm. Later researches demon- 
strated the fact that most cells are solid bodies, and in many 
cases — e.g. lymph-corpuscles — are naked portions of proto- 
plasm not possessing any distinct wall or peripheral membrane. 
It was thus clearly shown that the hollow vesicular condition 
and the presence of a cell-wall were not necessary to the cell, 
but that the protoplasmic content must be the basis of life. 
Somewhere within the protoplasm of the cell there is 
situated a definite, somewhat rounded body called the nucleus , 
and this nucleus may contain one or more smaller bodies 
called nucleoli. The earlier observers attached only a secondary 
importance to the nucleus, but the latest researches go to 
prove beyond a doubt that the nuclear material, whether col- 
lected into a single mass or scattered about as small particles, 
is always present, and that it is probably the most important 
part of the cell. Leydig and Max Schultze, thirty years ago, 
defined the cell as ‘ a mass of protoplasm containing a nucleus, 
that both nucleus and protoplasm arise through the division 
of the corresponding elements of a pre-existing cell,’ and it 
may be stated that this definition still holds good. 
I will devote a short space to the general morphology of 
the cell. An isolated cell is, roughly speaking, spherical, 
e.g. in unicellular plants and animals. In the great majority 
of cells the spherical form is altered by various conditions, such 
as movements of the cell-substance, the effects of mechanical 
pressure, &c. 
Protoplasm, which forms the basis of the cell, is a translucent 
viscid substance, at times appearing homogeneous, in other 
cases finely granular, giving as a rule the appearance of a net- 
work or 4 reticulum.’ In addition to this living active proto- 
plasm the cell almost universally contains certain lifeless bodies, 
which are found in the meshes of the network. Among such 
lifeless substances may be mentioned pigment bodies, drops 
