PROTOPLASM 113 
struction and efficiency as compared with microscopes of today, 
was beginning to be employed by Robert Hooke (1635-1703) 
and others in the seventeenth century in the study of plants. 
Robert Hooke, one of the earliest to study plants with the 
microscope, examined thin sections of cork, and found the cork 
to be composed of numerous small compartments which he 
called cells on account of their rough resemblance to the cells 
of a honeycomb. Of course in dead tissue like cork the cell 
contents are absent, and Robert Hooke saw only the cell walls 
enclosing the spaces from which the active substance of the 
cells had departed. However, through investigations which fol- 
lowed those of these earliest investigators with the microscope, 
it gradually came to be recognized that the important part of 
the cell is the substance which fills the compartments. By ex- 
tending the study to many kinds of tissues of both plants and 
animals, it was finally recognized that the substance filling the 
cell is the only living substance in plants and animals and the 
substance which builds the cell wall and the entire organism. 
Various names were at first applied to this substance before the 
term protoplasm suggested by Hugo Von Mohl was adopted by 
both botanists and zoologists. As the word protoplasm, which 
is a combination of protos (first) and plasma (thing formed), sig- 
nifies, this substance was considered the first organic substance 
formed from the inorganic materials taken into the plant. The 
idea that the protoplasm is the essential substance and that the 
cell is the unit of plant and animal structure was quite thoroughly 
elaborated by Schleiden (1838) and Schwann (1839) and became 
generally accepted. 
Protoplasm. — The protoplasm, as already noted, is the living 
substance of plants and animals. The protoplasm of an indi- 
vidual cell is often called a protoplast. Protopldsm is a fluid 
substance which varies much in its consistency, sometimes being 
a thin viscous fluid like the white of an egg, and sometimes being 
more dense and compactly organized. Chemical analyses show 
that protoplasm has the composition of protein, although such 
analyses necessarily kill the protoplasm and consequently do not 
give us a true knowledge of the protoplasm as it is while living. 
Although the protoplasm of higher plants usually exhibits no 
motion except when dividing, there are cases, however, as in the 
hairs of the Pumpkin and Wandering Jew, where the protoplasm, 
