Amoeba

a-me ba, plural amoebae, a low form of animal life found occasionally in fresh water. A dipper-full of water from the edge or bottom of a grassy, stagnant pool may contain hundreds of amoebae. An amoeba is so small that it cannot be seen with the naked eye. Examination of a drop of the water under a miscroscope is necessary for its identification. It is then found to be a particle of white jelly, having a somewhat granular central portion and an outer transparent part. When first seen, the amoeba may appear to be entirely motionless; but careful observation shows it to be constantly in motion, although it has neither head, tail, nor feet; nor eyes, ears, or nose. It moves about from place to place by thrusting any part of its body out into narrow but blunt projections, and then drawing in the projections which it does not need for advance.

When the amoeba is examined with a high power microscope, objects which otherwise would escape notice are seen within its substance. One of these is a small, rounded body, darker in color than the surrounding substance, and preserving its form at all times. This object is called the nucleus. The nucleus is made of protoplasm, just as is the entire body of the amoeba; but it is surrounded by a membrane and refracts light more strongly than the body of the amoeba. The other object seen is a clear, rounded space, apparently filled with a watery fluid. This is called a vacuole. It increases and then decreases in size many times during an hour, and is thought to expel a liquid which it receives from the surrounding protoplasm.

The amoeba is a type of the one-celled animals, for a particle of living protoplasm containing a nucleus is called a cell. It has no organs of any kind, except the nucleus and vacuole. Although so simple in its structure the amoeba grows, takes nourishment, digests and assimilates food, excretes waste matter, and produces other creatures like itself, as do the higher animals. Its food consists of very small one-celled plants, or of particles of higher plants or animals. It engulfs or envelopes a food-particle in the substance of its body, where it becomes surrounded by a watery globule and finally disappears. The indigestible part, if there is any, passes out of the body. That portion of the food which is retained is doubtless mixed with the substance of the body and adds to its size.

When an amoeba becomes full-grown, the nucleus divides into two nuclei. The protoplasmic body of the amoeba also divides in such a way that each part contains one of the nuclei, and in this way two amoebae are formed. When these two become full-grown, the same operation is repeated, so far as known indefinitely, so that the amoeba is sometimes said to be "immortal."

There are many species of amoebae, some harmless, others producing diseases (malaria, dysentery, etc.), if introduced into the body by drinking water or otherwise.