{ Xan"thine (?), n. Also Xan"thin }. [Gr. xanqo`s yellow.] (Physiol. Chem.) A white microcrystalline nitrogenous compound, C5H4O2N4, present in muscle tissue, in the liver, spleen, pancreas, and other organs, and also in urine (in small quantities) and some urinary calculi, and in the juices of certain plants; -- so called because it leaves a yellow residue when evaporated to dryness with nitric acid. Xanthine is closely related to uric acid.
Xan"tho*chroid (?), a. [See under Xanthrochroic, -oid.] (Ethnol.) Having a yellowish or fair complexion. -- n. A person having xanthochroid traits.
Xan*thoch"ro*ism (?), n. Abnormal coloration of feathers in which yellow replaces the normal color, as in certain parrots. It is commonly due to lack of the dark pigment which with yellow forms green.
Xan*thom"a*tous (?), a. (Med.) Of or pertaining to xanthoma.
Xan`tho*mel"a*nous (?), a. [Pref. xantho- + Gr. &?;, &?;, black.] (Ethnol.) Of or pertaining to the lighter division of the Melanochroi, or those races having an olive or yellow complexion and black hair.
Xen"on (?), n. [Gr. &?;, neut. of &?; strange.] (Chem.) A very heavy, inert gaseous element occurring in the atmosphere in the proportion of one volume is about 20 millions. It was discovered by Ramsay and Travers in 1898. It can be condensed to a liquid boiling at -109° C., and to a solid which volatilizes without melting. Symbol Xe or X; atomic weight 130.2.
XP (?). [Belongs here in appearance only.] The first two letters of the Greek word XRISTOS, Christ; -- an abbreviation used with the letters separate or, oftener, in a monogram, often inclosed in a circle, as a symbol or emblem of Christ. It use as an emblem was introduced by Constantine the Great, whence it is known as the Constantinian symbol, or monogram. See Labarum.
{ X rays, or X"-rays` (?) }, n. pl. The Röntgen rays; -- so called by their discoverer because of their enigmatical character.
X"-ray" tube. (Physics) A vacuum tube suitable for producing Röntgen rays.
Xy"lan (?), n. (Chem.) A gummy substance of the pentosan class, present in woody tissue, and yielding xylose on hydrolysis; wood gum.
Xy*lol"o*gy (?), n. [Pref. xylo- + -logy.] The branch of dendrology treating of the gross and minute structure of wood.
Xy"lose (?), n. [Pref. xylo- + -ose.] (Chem.) An unfermentable sugar of the pentose class, C5H10O5, formed by the hydrolysis of xylan; wood sugar.
Xy*lot"o*mist (?), n. One versed or engaged in xylotomy.
Xy*lot"o*mous (?), a. [Pref. xylo- + root of Gr. &?; to cut.] (Zoöl.) Capable of boring or cutting wood; -- said of many insects.
Xy*lot"o*my (?), n. [Pref. xylo- + -tomy.] Art of preparing sections (transverse, tangential, or radial) of wood, esp. by means of a microtome, for microscopic examination.
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