n the
structure of organic bodies. He classifies the parts as "similar" and
"organic," the former determined by their material, the latter by the
form which they assume. The similar parts are divided into the
sanguineous or rich in blood and the spermatic. Both sets are further
subdivided according to their physical characters,[18] the latter, for
instance, into the hard, soft, and tensile tissues. The classification
resembles greatly that propounded by Aristotle, though it is notably
inferior in the details of its working out.

For Aristotle, as for all anatomists before the days of the
microscope, the tissues were not much more than inorganic substances,
differing from one another in texture, in hardness, and other physical
properties. They possessed indeed properties, such as contractility,
which were not inorganic, but as far as their visible structure was
concerned there was little to raise them above the inorganic level.
The application of the microscope changed all that, for it revealed in
the tissues an organic structure as complex in its grade as the gross
and visible structure of the whole organism. Of the four men who first
made adequate use of the new aid, Malpighi, Hooke, Leeuenhoek, and
Swammerdam, the first-named contributed the most to make current the
new conceptions of organic structure. He studied in some detail the
development of the chick. He described the minute structure of the
lungs (1661), demonstrating for the first time, by his discovery of
the capillaries, the connection of the arteries with the veins. In his
work, _De viscerum structura_ (1666), he describes the histology of
the spleen, the kidney, the liver, and the cortex of the brain,
establishing among other things the fact that the liver was really a
conglomerate gland, and discovering the Malpighian bodies in the
kidney. This work was done on a broad comparative basis. "Since in the
higher, more perfect, red-blooded animals, the simplicity of their
structure is wont to be involved by many obscurities, it is necessary
that we should approach the subject by the observation of the lower,
imperfect animals."[19] So he wrote in the _De viscerum structura_, and
accordingly he studied the liver first in the snail, then in fishes,
reptiles, mammals, and finally man. In the introduction to his
_Anatome plantarum_ (1675), in which he laid the foundations of plant
histology, he vindicates the comparative method in the following
words:--"In the e