Page:A Text-book of Animal Physiology.djvu/31



(βιος, life; λογος, a dissertation) is the science which treats of the nature of living things; and, since the properties of plants and animals can not be explained without some knowledge of their form, this science includes morphology (μορφη, form; λογος, a dissertation) as well as physiology {φυσις, nature; λογος).

Morphology describes the various forms of living things and their parts; physiology, their action or function.

General biology treats neither of animals nor plants exclusively. Its province is neither zoölogy nor botany; but it attempts to define what is common to all living things. Its aim is to determine the properties of organic beings as such, rather than to classify or to give an exhaustive account of either animals or plants. Manifestly, before this can be done, living things, both animal and vegetable, must be carefully compared, otherwise it would be impossible to recognize differences and resemblances; in other words, to ascertain what they have in common.

When only the highest animals and plants are contemplated, the differences between them seem so vast that they appear to have, at first sight, nothing in common but that they are living: between a tree and a dog an infant can discriminate; but there are microscopic forms of life that thus far defy the most learned to say whether they belong to the animal or the vegetable world. As we descend in the organic series, the lines of distinction grow fainter, till they seem finally to all but disappear.

But let us first inquire: What are the determining 1