DIASTASE, 208 DIATOMACE^. and ether. and dryiiiji;. The powder so obtained may be still lurther puiitied by !<o!utiou iu water, refiiifipitation with alcohol, and dialysis. In llie dry --tale, it may be kept iudelinitely, and retains" its digestive power. The aetion of diastase on starch is one o{ hydrolysis, i.e. it causes the starch to combine with water and break up into simpler com- pounds. Tlic intermediate ste|)s in the process are not known. i'.ut the ultimate products of tho hydndysis are a variety of suyar called maltose, !S0 |>er cent., and de.xtrin (q.v.), 20 per cent. Diastase acts most ellectively in a weak solution of common salt and carbonic acid, both of which are ordinarily present in planteclls. The pres- ence of antiseptics, as well as of alkalies, acids, and many salts, has the elTect of greatly diniin- i>hing and sometimes of altogether destroying the ellicacy of the enzyme. Diastase is largely made use of in the manu- facture of beer and alcohol, small quantities of the enzyme being capable of elVecting the trans- formation of a considerable amount of starch. A preparation of diastase has of late also been used with some success in the treatment of fer- mentative dyspepsia. See Alcouol; Beeb; Dex- trin: Knzvmi;s. DIAS'TROPHISM. A general term applied to the geological processes which cause the up- heaval and subsidence of continental lands and the building of mountain systems. Such proc- esses probably result from the strains produced in the earth's crust in adjusting itself to the nucleus. See Geology: Coxtixkxt; Mouxt.in. DIATHER'MANCY (from Sid, dia, through + e^piui^ffti, lluiiiiaiisis, a beating, from dep- fialyety, tlurmainciii, to heat, from depiiii, thei- tiios, warm: connected with Lat. furiiui.s, Skt. yharma, hot ) . A term used to e.vpress that qual- ity of a body in virtue of which those ethcr- vaves are allowed to pass which produce thermal effects to a marked degree: it may, in general language, be called 'transparency to heat.' All ether-waves carry energy: and in many cases when these waves are absorbed their energy is spent in producing beat efTects. (This is not so, of course, when the energy of the waves goes to chemical or electrical action.) It is found that in the spectrum of ether-waves emitted by any body, r.s. the sun. the energy carried by waves of different wavciiundicr is in general different; similarly, the transparency of a body to ether- waves varies with their wave-number. In dis- cussing diathcrmancv. therefore, it is necessary to consider both the total radiation transmitted and also the wave-nuud)ers of these waves, (fye R.Di.TioN.) In general terms, the greater por- tion of the energy carried from the sun and from other bodies by ether-waves is associated with waves whose wave-numbers are so small that they do not affect our sense of sight: and other instrument- have to be used to detect the waves and measure their energv-. Such are thermometers, bolometers, radio-micrometers, radiometers, etc. It is possible to have bodies which arc absolutely opaque to those waves which affect our eyes, and yet are transparent to waves which have a less wnvenundHT: and the converse is true. The diathernuincy of a body depends upon its tein- perature anpositioii. Iroin dioritftaeoi, itinlitlwslhiii, to dispose, from Sid, iliu, apart + nWcat, litlicnui, to plac-e). A word applied in medicine to the predisposition or constitution of the body which renders it prone to certain diseased states. Thus the tubercular, scrofulous, gouty, rheumatic, can- cerous, or hemorrhagic diatheses arc mentioned. A person with gouty diathesis is one in whose case exposure to cold, eating indigestible food in large quantities, or drinking beer cause-) gouty pains and increased amount of uric acid in the urine; who is likely to have eczema; whose blood is deficient in luvmoglobin : and whose arteries are inelastic. The study of diathesis is of great importance, as avoidance of disease through choice of occupation and habits is often possible, if predisposition to disease is recog- nized. DI'ATOMA'CE.ffi (XeoLat. nom. A. from Gk. SiaTOMi), ili'iloiiii-, severance, from SuiT^tiKip, diaicnnK in, to cut through, from Std, Jin, through + Tttivtiv, (emnein, to cut). .
inunensc group
of unicellular alga", estimated at 10,000 species. The cells are solitary or united in various ways into colonies that "are frequently elaborately branched. Each cell is provided with a siliceous shell in two halves, which lit closely together. These shells, called valves, are exquisitely sculp- tured and make favorite preiiarations for the amateur microscopist. Many diatoms have power of movement, although the cells are never pro- vided with cilia. They slide rapidly backward aiul forward in a way that is not well under- stood. The structure and distrilmti<m of the cell contents in the diatoms suggest the structure of desmids (q.v.), but the color is generally brown Cendochrome'). Owing to i-ertain peculiarities of cell-division, it is necessary that diatoms at certain periods pass into a resting stage, in which the protoplasm prepares for a new periiwl of vegetative activity. This resting stagi" is called an auxospore. In some eases the cells change directly into auxospores, but in a large proportion of forms the auxospores result from the fusion of the cell contents of two diatoms. This union of protoplasm does not always pre- sent the characters of a sexual act, but it is
