Amœ'ba, one of the lowest microscopic animal organisms, extensively used in laboratory work in biology. The amœba is a single cell (see Cell Doctrine); its body is a mass of protoplasm. Therefore, when we make observations upon it we are observing protoplasm at first hand and can determine its properties and behavior. Within its body all the physiological acts take place in a simplified form. It is, therefore, of unusual interest to biologists, for the physiological processes are so complex in higher animals that one must have them reduced to their simplest expression in order to comprehend them. The soft protoplasm of its body is always moving. It flows into finger-like processes (pseudopodia), and changes its position from place to place. It also flows about food particles and thereby engulfs them into its substance. The amoeba is found in stagnant water, moist moss, etc. The living substance of its body is contractile, like muscles; irritable, like nervous tissue; receptive, assimilative, respiratory, reproductive, etc.—the germs of activities that are more developed and perfected in higher animals. See Protozoa.
