Page:The New International Encyclopædia 1st ed. v. 12.djvu/184

* LEXTCKAKT. 166 LEUCOPLASTS. vnd den feineren Bau dcr fichleimhaui bei dm In- sectencicrn (1855); Die Blascnhandioiirmcr (1856); Vnterstichungen uber Trichina Spiralis (18(i0) ; Die Parasilin <hs .l/cMSc/irn, etc. (1803- 70); Zonlogische Wandtafcin (1877-98); Ueber die h'.nticickeUtng tier Sphaerularia Bombi (1885). Leuckart's fame as a zoologist and ti'aclipr was very great. LEU'COCYTE ( from Gk. cvk6s, leukos, white -j- Kirus, ki/los. cell). . lymphoid or amoelioid itll. The name is generally applied to lymjjli- eells outside the blood-vessels, and to the white corpiiseles of the blood (q.v. ). The source of the wliite cells of the blood is undoubtedly the lymphatic glands as well as the bone-iuarrow. the spleen, and the gastro-intestinal lym])hfolli- cles. LET:'COCYTH.a)'MIA (Neo-Lat.. from Gk. Xd'Kiij, leukos, white + Kiros, kytos, cell + a'l/ia, liuima, blood). A disease characterized by an in- crease in the number of white corpuscles in the blood, together with cliaiigcs in the bone-marrow, spleen, and lymphatic glands. The disease was first noted by Bennett of Kdiuburgh, who con- sidend the affection diu' to the presence of pus in the blood, and gave it its name. In the same year Virchow of Wiirzburg published his ob.serva- tions u])on the disease and was the first accu- rately to recognize and describe it. He gave it the name 'leukirmia.' 'irchow's theory of the pathogenesis has been adopted, viz., that it is pri- marily a disease of the blood making organs, and that the conditions of the blood are secondary. The disease is common among the working classes, and the majority of the cases occur be- tween the twentieth and fiftieth years. It is twice as common among men as among women. Ma- laria, syphilis, and traumatism are supposed to have influence as |)redisposing causes; but there is great reason to believe that the disease is essen- tially infectious in its nature. The symptoms of the disease are pallor, or an ashen color; pal- pitation of the heart ; ilys[)n(i'a upon exertion: en- largement of the lymphatic glands, in bunches, most frequently in the neck : great enlargement of the spleen, with tenderness in the splenic re- gion: enlargement of the liver; diarrhoea: nerv- ous disturbances, including headache. languor, depression, delirium, or even mania; a tendency to ha'niorrhage ; deafness, and vertigo. An exam- ination of the blood will readily determine the presence of the disease, and will decide whether the case in hand is of the myelogenous or the lymphatic variety of the disease. In the former, which is the more frequent form, there is an ex- cess of the large mononuclear cells, especially of ihc myelocrtes; and also large numbers of nucle- ated red corpuscles, notably of megaloblasts. In the lymphatic variety there is an Jinusual propor- tion of lymphocytes of the ordinary variety, or rather large, with paler nuclei and almost wholly withoiit granules: while mvelocvtes and nucle- ated red corpuscles are present in very small numbers. Leucocythtemia is almost invariably fatal. The disease may run a course of from five to eight years, though the average duration is less than three years. Amelioration of the symp- toms may be secured by treatment in some cases. Freedom from care, change of climate, a diet in which carbohydrates and fats are prominent, arsenic, quinine, bone-marrow, bitter tonics, and iron are all serviceable. Cold douches to the splenic region as well as faradization or galvani- zation of this region have relieved the pain or dis- C(jmfort experienced there. Anorexia, indiges- tion, constipation, and diarrhcea demand special treatment. Consult Ehrlich. Leitk'iimie, Pseudo- lrllk^il)lir. fHimoqlohinuric (Vienna, 1001). LEUCOLINE, in'krt-lln. See Quinoline. LEUCO'MA (Xeo-Lat., from Gk. X^ku/xo, IriikOmii, white spot in the eye. from 'Kcvkovv, leu- loiiii, to whiten, from evK6$, leukos, white). The term applied to a white opacity of the cornea. It is also called albugo. It is the result of acute inflammation, giving rise to the deposition of eo-. agulablc lymph on the sirface, or between tha layers of the cornea. It is sometimes reabsorbed on the cessation of the inflammation, and the cor- nea riK'overs its transparency ; but in many cases it is persistent and incurable. It may also be the result of previous ulceration or of injury to the cornea. The mildi'st degree of opacity is kno^^■n as nebula, and a grade intermediate be- twwn this and leucoma as macula. When per- foration of the cornea is followed by adhesion of the iris to the resultant scar, the condition is spoken of as adherent leucoma. LETT'COPLASTS (from Gk. evK6s, leukos, while -- TracT6s. iiluslos. formed, from TrXdtrtretv, pliissein, to form). Minute colorless bodies (also called Amyloplasts), whose special function it is to accumulate starch and sometimes proteids into solid granular form. They are special or- gans of the protoplasm in active plant-cells. Sim- ilar to these are the plastids. including chromo- plasts and chloroplasts (qq.v. ). They may occur in any cell, but are mostly readily ob- served, because most abundant, in cells devoted to storage of reserve food. The starch-forming Icucoplasts absorb the dissolved material (sugar?), convert it into starch, and begin to deposit this starch in their interior (see figure). The mature starch-grain is usually oval or round- STABCH-SRilNS (WBITE) FORMISB INSIDE LECCOPLASTS. a, An eccentric Krain, with the bulk of the leucoplast on one end ; b, a younger stage of the eame. i.sh, rarely irregular. Structurally it is a sphere crystal, being composed of minute hair-like crys- tals (trichiles), which radiate from a centre. Additions to the starch-grain, as it is growing, are made exclusively upon its surface. As the starch-grain increases in size in the interior of the leucoplast. the latter is stretched. If the grain originates in the centre of the leucoplast the stretching may be uniform, in which case nearly equal layers may be added to all sides. More often, however, it arises eccentrically, and