AL'TERATIVE ( Lat. alter, other, another, different). In medicine, a term applied to rem- edies that have been found to act slowly and in an unknown way. improving the nutrition of the body. It is generally applied to medicines which are irritant in full doses, but which almost im- perceptibly alter disordered actions or secre- tions; acting specially on certain glands, or upon absorption in general, when they are given in com- paratively small doses, the treatment being con- tinued for a considerable length of time. For ex- ample, mercury is an irritant in some of its prep- arations; but when small doses of some of its preparations are given at intervals for some length of time, they "produce alteration in disor- dered actions, so as to cause an improvement in the nutrient and digestive functions, the disap- pearance of eruptions, and the removal of thick- ening of the skin or of other tissues" (Royle); and they will effect these changes without other- wise affecting the constitution or inducing sali- vation. So iodine, also an irritant in concen- trated doses, and poisonous in some forms, is most useful when given in small doses in certain enlargements of glands, and need not cause iodism, if carefully given. The most marked example of the alterative action of mercury and the iodides is seen in cases of syphilis.
Some preparations of arsenic are powerful alteratives in eases of skin disease. Cod liver oil (q.v.) is an alterative which is used with great benefit in tuberculous conditions, rickets, and other diseases which are associated with poor nutrition. Preparations of phosphorus have a powerful alterative action. Colchicine (q.v.) is said to act in this way in gout and subacute rheumatism. Ichthyol (q.v.) is an important alterative in skin affections when applied locally. Sarsaparilla (q.v.) was formerly believed to possess strong alterative qualities, but it has been shown to be practically inert.
ALTER (iil'ter) FRITZ (Ger., Old Fritz).
A popular designation of Frederick the Great.
ALTERNATING (al'ter-na'ting) CUR'RENTS. See Electricity, and Dynamo-Electric Machinery.
AL'TERNA'TION OF GEN'ERA'TIONS (Lat. alternatio, an interchange, from alter, other, and generation from genus, birth, descent, offspring). The successive occurrence in one life-cycle of two or more dissimilar forms; the process by which in its life history a plant or
animal may pass through alternating phases
that do not resemble one another, especially
differing in being successively sexual and asex-
ual. This phenomenon is very widespread
among organisms, and assumes different charac-
ters in different groups of plants or animals.
Among Plants. Alternation of generations is
found in all forms of plants excepting the low-
est, though it is not very evident in the highest
plants. One may get some conception of alter-
nation of generations in plants by comparing it
with the very different alternation of forms
which occurs in the life history of a moth or
butterfly. In the plant, however, instead of
having a series of forms which pass into one
another, our plant larva forms an egg which
produces the mature form. If in the life his-
tory of a butterfly the larva should lay eggs and
thus produce the mature forms, we should have
something resembling the alternation of genera-
tions in plants. One of these generations has
sex organs, and hence is called the gametophyte; while the other generation has no sex organs, and is known as the sporophyte. Both generations produce spores, but in a very different way. By means of its sex organs the gametophyte produces spores in a sexual way, that is, by the fusion of two sex cells, and such spores are called in general oöspores, or fertilized eggs; while the sporophyte by ordinary cell division produces spores which are called asexual spores, meaning spores which have not been formed by sex organs. In the life history of the plant, the sexual spore of the gametophyte gives rise to the sporophyte, while the asexual spore of the sporophyte gives rise, in turn, to the gametophyte. and so the alternation continues.
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Life history of a Moss: 1, the gametophyte, with the protonema (p) developed from an asexual spore (y), and giving rise to buds (b) that develop the leafy shoot (s); 2, the young sporophyte (c) rising above the leafy shoot (s).
Alternation of generations is first manifested among the lowest plants (the thallophytes),
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Sporophyte (sporogoninm) of a moss: 1, the young sporo- phyte (e) rnpturhlg the calyplia, carrying up the cap-lil«e upper portion (t'(;;.', a mature sporopliyte. showing imbedded foot (f), seta (y), capsule (c), and operculum (o).
but it is not completely and clearly established until the liverworts and mosses (bryophytes) are reached. The phenomenon is still more
