26 DISCOVERY OF PROTOPLASM. 
continuous coat, and, so to speak, builds itself a little chamber wherein to live. We 
may therefore distinguish naked protoplasm from that kind which inhabits the 
interior of a cell of its own creation, and compare the former to a shell-less snail, 
and the latter to a snail that constructs the house in which its life is spent. Still 
better may we compare the firm and solid cell-membrane with which the protoplasm 
clothes itself to a protective coat, a garment fitted to the body; and, following out 
this analogy, the protoplasm must be designated the living entity in the cell, and 
the secreted envelope must be considered as merely the skin of the cell. Conse- 
quently, although this cell-wall was the part which was first revealed by magni- 
fying glasses, and was called a cell on account of its form, this is not the essential 
formative element, which has the power of nourishing and reproducing itself. 
It is the body within the cell, the slimy, colourless protoplasm in full activity within 
the surrounding membrane made by itself, which must be taken to be the essential 
part of the cell and the basis of life. 
The term cell had become so naturalized in the science that protoplasm which 
had escaped from a cell-cavity was also called a cell, and the unfortunate name of 
“naked cell” was brought into use to designate it. More recently many of these 
older designations have been abandoned as unsuitable. We now include under 
the term “protoplasts” all these individual organisms, consisting of protoplasm, 
which occupy little chambers made by themselves, living either alone like hermits or 
side by side in sociable alliance in more or less extensive structures, able under 
certain circumstances to leave their domiciles, laying aside their envelopes and 
swimming about as naked globules. 
Only when the protoplasts live in innumerable little cavities congregated close 
together in colonies, and when these cavities are bounded by even walls and are for 
the most part uniformly developed in all directions, does the part of a plant com- 
posed of them look under the microscope like a honey-comb, and each cavity like a 
cell. But even in these cases of external similarity there is the essential difference 
that in a honey-comb each of the walls separating individual cells is common to both 
the adjacent spaces, and, accordingly, the cells of the comb are like excavations in a 
continuous matrix; whereas, in sections of cellular plants, every cell possesses its own 
particular and independent wall, so that in them every partition-wall between 
neighbouring cavities is composed, properly speaking, of two layers (fig. 6). 
These two layers are scarcely distinguishable in the case of delicate cell-membranes 
newly secreted by the protoplasts. Later on, however, they are always to be made 
out clearly (fig. 6°). Frequently the layers separate one from another at certain 
spots, and thus channels are formed between the cells (fig. 6 *); these are called “ inter- 
cellular spaces.” One often sees cells, too, whose entire surfaces are, as it were, 
glued together with a kind of cement, and then this substance which is stored 
between the two layers is called “intercellular substance” (fig. 6°). 
By loosening the intercellular substance, where present, by mechanical or chemi- 
cal means, we can easily separate adjacent cells from one another; the two layers 
of the partitioning cell-walls come asunder, and then each separate cell exhibits a 
