PROTOPLASM, THE PHYSICAL BASIS OF LIFE The recognition of the rôle that protoplasm plays in the living world was so far-reaching in its results that we take up for separate consideration the history of its discovery. Although it is not yet fifty years since Max Schultze established the protoplasm doctrine, it has already had the greatest influence upon the progress of biology. To the consideration of protoplasm in the previous chapter should be added an account of the conditions of its discovery, and of the personality and views of the men whose privilege it was to bring the protoplasm idea to its logical conclusion. Before doing so, however, we shall look at the nature of protoplasm itself. Protoplasm.--This substance, which is the seat of all vital activity, was designated by Huxley "the physical basis of life," a graphic expression which brings before the mind the central fact that life is manifested in a material substratum by which it is conditioned. All that biologists have been able to discover regarding life has been derived from the observation of that material substratum. It is not difficult, with the help of a microscope, to get a view of protoplasmic activity, and that which was so laboriously made known about 1860 is now shown annually to students beginning biology. Inasmuch as all living organisms contain protoplasm, one has a wide range of choice in selecting the plant or the animal upon which to make observations. We may, for illustration, take one of the simplest of animal organisms, the amoeba, and place it under the high powers of the microscope. This little animal consists almost entirely of a lump of living jelly. Within the living substance of which its body is composed all the vital activities characteristic of higher animals are going on, but they are manifested in simpler form. These manifestations differ only in degree of development, not in kind, from those we see in bodies of higher organisms. We can watch the movements in this amoeba, determine at first hand its inherent qualities, and then draw up a sort of catalogue of its vital properties. We notice an almost continual flux of the viscid substance, by means of which it is able to alter its form and to change its position. This quality is called that of contractility. In its essential nature it is like the protoplasmic movement that takes place in a contracting muscle. We find also that the substance of the amoeba responds to stimulations--such as touching it with a bristle, or heating it, or sending through it a light electric shock. This response is quite independent of the contractility, and by physiologists is designated the property of being irritable.