Page:The New International Encyclopædia 1st ed. v. 01.djvu/559

AMMUNITION WAGON. AMMUNITION WAG'ON. A specially built wagon for the safe and speedy transport of ammunition. The general use of rapid-fire guns has made the question of suitable wagons, capable of carrying the tremendous quantities of ammunition demanded by modern arms and warfare, one of the most important features of a campaign. It is worthy of note that Lord Roberts, the British commander-in-chief in the Boer War, specially employed and strongly recommended wagons built in the United States and used generally in the United States Army. The important features of such wagons are great strength, easy draught, great flexibility, and adjusted balance. They must also be so arranged that the shells and fuzes are held firmly in place, and secured as strongly as possible against shocks and jolts or damage by water.

AM'NESTY (Gk. a/ivi/aria, amnCstia, forget- fulness, from a, o, priv. + ^ivuo-dai, ministhui, to remember). An act of State granting oblivion for past offenses, and generally employed where pardon (q.v. ) is extended to whole classes or communities instead of to individuals before trial and conviction. The President may grant amnesty by a general proclamation for offenses against the United States, except in cases of im- peachment; and the Supreme Court has held that Congress also may pass acts of general am- nesty. (Brown vs. Walker, 161 U. S. 591. [1895].) There was a vigorous dissent, however, in this case.

AM'NION (Gk. ἀμνίον.). The membrane which immediately invests the embryo, appearing very early in the development of the latter, and adhering closely to it. As gestation proceeds, this membrane secretes from its inner surface a fluid which separates it from the fœtus. This fluid, the liquor amnii, supports and at the same time gives free movement to the fœtus, preserves it from injury, and maintains around it an equable temperature, and later, during labor, becomes, with its inclosing membranes, an important dilator of the genital canal. See, and.

AMNIO'TA. See.

AMŒ'BA (Neo-Lat.; Gk. ἀμοιβή, amoibē, change, alternation). A microscopic animalcule, classified among the lowest Protozoa, which in- habits fresh water or occasionally moist earth. It appears in water under great magnification as a clear, translucent, highly refracting body. It is made up of a substance that docs not mix with water, is viscid like glue, and has a specific gravity a little greater than water, namely about 1.015. Under the highest power of the microscope, particularly after death, the body is seen not to be perfectly homogeneous, but to be made up of films inclosing water-filled spaces. This structure may be imitated by making a fine mixture of oil and potassium carbonate, and letting it stand in water. The potassium carbon- ate is hygroscopic, and eventually an emulsion is produced in which the oil stands to the water in the same relation that the protoplasmic films do to the water spaces. The cytoplasm is not all of the same kind. Near the centre is a special- ized portion known as the nucleus, the proto- plasm outside of which is called cytoplasm. Be- tween nucleus and cytoplasm a constant inter- change of material is taking place in the living cell, and the two parts are interdependent.

A living amœba under appropriate conditions exhibits a continual movement of the protoplasm. The very structure favors a constant movement, as witness the artificial emulsion, whose outline is constantly changing. In amœba processes (pseudopodia) are thrust out at certain points of the body, and others behind them are re- tracted, and thus a change occurs in the centre of the mass and locomotion is effected. Amœba is irritable, i.e., it is affected in a definite man- ner by external conditions; it "responds" to them by moving with reference to them. With- out a stimulus there would probably be no move- ment at all. If the stimulus comes upon the or- ganism from one side, it may move toward or from that side. Thus the amœba moves from the point of contact of a needle or from the source of light, or it moves so as to keep in water of a medium temperature. Thus we see that pro- toplasm early had the capacity of appreciating external conditions and moving with reference to them. This may be regarded as the beginning of a "psychic life."

AMŒBA Beginning at the upper left-hand figure, the successive drawings show the progress of a division of an amœba through its nucleus into two.

The amœba is, by its movements, constantly expending energy. This must be renewed by taking in fuel. Also, its plasma is undergoing constant destruction and must be reformed. Food here serves two purposes. (1) It serves as fuel. (2) It forms new protoplasm. But these two rôles may be played by the same food-stuff. There is no proper oral aperture, and the food is merely taken into the interior of the body by a process of intussusception — any portion of the surface being chosen for this purpose, and acting as an extemporaneous mouth. Sometimes the ingestion of food takes place chiefly at the posterior end of the body. When the particle of food has been received into the body, the aperture by which it was admitted again closes up, and the discharge of solid excreta is effected in an exactly similar but reverse manner. Food-stuffs that are ingested become dissolved (digested) and penetrate the plasm films. Here they are burned (oxidized) and carbon dioxide, water, urea, and other substances are produced. These get back into the water spaces and are finally thrown out