An´iline, C6H5NH2, is an extremely important substance as it forms the starting-point in the preparation of a large number of substances. It was first prepared by Unverdorben, in 1826, by distillation of indigo. Aniline is present in small quantity in coal-tar, and is prepared commercially from benzene by transforming it by means of nitric acid into nitro-benzene and reducing this with scrap-iron and hydrochloric acid. The substance can also be prepared by reducing nitro-benzene electrolytically. It is a liquid of peculiar odour, boiling at 182° C., colourless when quite pure, but rapidly darkening in colour on standing, so that commercial aniline is usually dark-brown. It is a basic substance, and forms crystalline salts with acids. The salts, like aniline itself, become coloured on exposure to air. Aniline contains the characteristic chemical group NH2, the amino group, and substances containing this group react with nitrous acid at 0° C., forming diazonium compounds; these combine readily with phenols, naphthols, and other amino compounds to form azo compounds, highly-coloured compounds many of which are dyes. Many dyes are prepared from aniline, e.g. rosaniline, magenta, methylene blue, aniline blue, &c., also some explosives, e.g. tetranitraniline, which is a powerful explosive prepared by nitrating aniline and the substance tetranitromethylaniline,
"tetryl", used in detonators. Several medicinal substances are also prepared from aniline, for instance, antifebrin and atoxyl.
An´ilism, aniline poisoning, a name given to the aggregate of symptoms which often show themselves in those employed in aniline works, resulting from the inhalation of aniline vapours. It may be either acute or chronic. In a slight attack of the former kind, the lips, cheeks, and ears become of a bluish colour, and the person's walk may be unsteady; in severe cases there is loss of consciousness. Chronic anilism is accompanied by derangement of the digestive organs and of the nervous system, headaches, eruptions on the skin, muscular weakness, &c.
Animal, an organized and sentient living being. Life in the earlier periods of natural history was attributed almost exclusively to animals. With the progress of science, however, it was extended to plants. In the case of the higher animals and plants there is no difficulty in assigning the individual to one of the two great kingdoms of organic nature, but in their lowest manifestations the vegetable and animal kingdoms are brought into such immediate contact that it becomes almost impossible to assign them precise limits, and to say with certainty where the one begins and the other ends. From form no absolute distinction can be fixed between animals and plants. Many animals, such as the sea-shrubs, sea-mats, &c., so resemble plants in external appearance that they were, and even yet popularly are, looked upon as such. With regard to internal structure no line of demarcation can be laid down, all plants and animals being, in this respect, fundamentally similar; that is, alike composed of molecular, cellular, and fibrous tissues. Neither are the chemical characters of animal and vegetable substances more distinct. Animals contain in their tissues and fluids a larger proportion of nitrogen than plants, whilst plants are richer in carbonaceous compounds than the former. In some animals, moreover, substances almost exclusively confined to plants are found. Thus the outer wall of the Sea-squirts contains cellulose, a substance largely found in plant-tissues; whilst chlorophyll, the colouring-matter of plants, occurs in Hydra and many other lower animals. Power of motion, again, though broadly distinctive of animals, cannot be said to be absolutely characteristic of them. Thus many animals, as oysters, sponges, corals, &c., in their mature condition are rooted or fixed, while the embryos of many plants, together with numerous fully-developed forms, are endowed with locomotive power by means of vibratile, hair-like processes called cilia. The distinctive points between animals and plants which are most to be relied on are those derived from the nature and mode of assimilation of the food. Plants feed on inorganic matters, consisting of water, ammonia, carbonic acid, and mineral matters. They can only take in food which is presented to them in a liquid or gaseous state. The exceptions to these rules are found chiefly in the case of plants which live parasitically on other plants or animals, in which cases the plant may be said to feed on organic matters, represented by the juices of their hosts. Animals, on the contrary, require organized matters for food. They feed either upon plants or upon other animals. But even carnivorous animals can be shown to be dependent upon plants for subsistence; since the animals upon which Carnivora prey are in their turn supported by plants. Animals, further, can subsist on solid food in addition to liquids and gases; but many animals (such as the Tapeworms) live by the mere imbibition of fluids which are absorbed by their tissues, such forms possessing no distinct digestive system. Animals require a due supply of oxygen gas for their sustenance, this gas being used in respiration. Plants, on the contrary, require carbonic acid. The animal exhales or gives out carbonic acid as the part result of its tissue-waste, whilst the plant, taking in this gas, is enabled to decompose it into its constituent carbon and oxygen. The plant retains the former for the uses of its economy, and liberates the oxygen, which is thus restored to the atmosphere for the use of the animal. Animals receive their food into the interior of their bodies, and assimilation takes place in their internal surfaces. Plants, on the other hand, receive their food into their external surfaces, and assimilation is effected in the external parts, as is exemplified in the leaf-surfaces under the influence of sunlight. Cf. T. J. Parker and W. A. Haswell, Text-Book of Zoology; Cambridge Natural History.
Animal Chemistry. See Chemistry.
Animalcule (an-i-mal´kūl), a general name given to many forms of animal life from their minute size. The larger examples are just visible to the naked eye, but most of them are strictly microscopic. Some are pigmented, but the majority are colourless. The term is not applicable to a particular zoological type, but it is customary to confine it to the 'Protozoa', 'Rotifera', or 'Wheel Animalcules'.
Animal Heat. All animals possess a certain amount of heat or temperature which is necessary for the performance of vital action. The only classes of animals in which a constantly-elevated temperature is kept up are birds and mammals. The bodily heat of the former varies from 39.4° to 43.9° C., and of the latter from 35.5° to 40.5° C. The mean or average heat of the human body is about 99° F., and it never falls much below this in health. Below birds, animals are named 'cold-blooded', this term meaning in its
strictly-physiological sense that their temperature is usually that of the medium in which they live, and that it varies with that of the surrounding medium. The temperature of 'warm-blooded' animals is remarkably constant, although there are individual variations. In man this variation is slight, amounting only to fractions of a degree. The cause of the evolution of heat in the animal body is referred to the union (by a process resembling ordinary combustion) of the carbon and hydrogen of the system with the oxygen taken in from the air in the process of respiration.
Animal Magnetism. See Hypnotism, Mesmer.
Animals, Cruelty to, an offence against which societies have been formed and laws passed in England and other countries. According to English law, if any person shall cruelly beat, ill-treat, overdrive, abuse, or torture any domestic animal, he shall forfeit a sum not exceeding £5 for every such offence. Bull-baiting, cock-fighting, and the like are also prohibited. Provision is also made for the punishment of persons unlawfully and maliciously killing, maiming, or wounding cattle, dogs, birds, beasts, and other animals.