788 



PARASITIC DISEASES 



PARCHMENT 



SM ASCARIS, BOT. BoTHRi'>cr.rHALrs, COMMEMSAI.IKM, 

 OOMI iMBBcrs, umiNEKATKiN. RmaanqoR, FISH- 

 LOUSE, FLUKE, GALLS, GRKUARINIHA. UUINKA-WDHM, 

 HAO, LEECH. LOUSE, Mirr, TAPEWORMS. THREAD- 

 WORMS, TRICHINA; lo Leuckrt, /'am*m </ iltntcten 

 (2J ed. 1881 rt v- . trmn.. br Hi.yle, voL i. Edin. 1886); 

 Kuchenraeirt-r, J'anuilen <itt lUrntfhtn (2d ed. 1H78; 

 tnuu. Ray Society); Cobhold, Paratittt (187); V*n 

 Beneden. Km Intntinaujc (Pwi., 1S5S). ^HI*M/ /Vim- 

 lila and Mtvmata (Inter. So. Sericn, Land. IS7(! I; V..n 

 Liiutow, CbMMiufiiMi </rr Httmintkologit ( 1878) ; Monies, 

 ia Pararir, dt CHommt ( 1888). 



Parasitic Diseases constitute an important 

 uu-group in the accepted clasMiication f IHsease 

 (q.v.). In these disease* certain morbid conditions 

 re induced by the presence of animals or vege- 

 tables which nave found a place of subsistence 

 within some tissue or organ, or upon some surface 

 of the body of man or other animals. Plants 

 are not exempt from disorders of this nature 

 (see PARASITIC PI.VNTS). The forms of animal 

 life giving rii' to parasitic diseases are dwenbcd in 

 article* on Ascarw, Cestoid Worms, Flea, Guinea- 

 worm, Itch, Lin-. Nematlielmia. Strongylus, Tape- 

 worms, Thread worms. Tick, Trichina, &c. 



The vegetable organisms which are associated 

 with special diseases are almost all of microscoiiic 

 size, and then-fore, though their effects are of much 

 greater importance than those of animal parasite*, 

 they are as yet much less perfectly understood. 

 Certain minute fungi have long been recognised 

 as the causes of diseases in the skin and mucous 

 membranes: Favus, Pityriasis versicolor, 1. ing- 

 worm. Thrush (q.v.). It was shown in 18(il by 

 Carter that a serious disease of the foot which 

 occurs in India (Madam-foot; fungus-fo.it, &c.) is 

 due to the presence of a fungus ; and in 1877 what 

 is now called Actinomycosis (q.v.) was put in the 

 same category. 



But the most important and interesting of the 

 vegetable parasites are those belonging to the 

 Scliizomycetes or Bacteria (q.v.), whose study has 

 assumed such (imminence that it is now almost 

 a independent science (Bacteriology). The rela- 

 tions of these organisms to their host are much 

 more intimate than in the case of the larger para- 

 site*, and the problems presented by the diseases 

 associated with them are consequently much more 

 difficult of solution ; but in some cases the parasitic 

 nature of tip--- diseases has been completely estab- 

 lished. Analogv niiikes it probable tliat some day 

 all 'specific febrile diseases' will have to be in- 

 cluded in this K roil p. S.-e CKKM TlJEOKV. 



Parasitic Plants are those which, unable to 

 nourish themselves, prey upon other plants or 

 animals ; becoming attached, they gain access to 

 the timues of their host and feed upon its juio-. 

 They are more or less degenerate, according to the 

 extent of their parasitism. Any cliiuliiiig plant 

 is no far a parasite, but, not drawing any nourish- 

 ment from its host, merely using it as a *upport, 

 .11 lii'- without it, and is perfect in all it* parts. 

 Many parasites have probably developed from such 

 plant*. The mistletoe, on the other hand, has no 

 root* in the ground ; its seed is left by a binl 

 upon an ap|ile or an oak tree, to which, when it 

 begins to grow, it U-cotncs attached by means of 

 pecial organs called haiistoria, which act as roots 

 and enable it to draw cnide sap, water, ami suits 

 from it host, and having green leaven it can alisorb 

 carUmic acid from the nir. and elaborate food for 

 its tinsnes. In the case of the dodder, again, which 

 begin* life us an indeiiendent plant, the seed ger- 

 minate* underground : when the young plant reaches 

 the surface it fastens upon some host, twining 

 round it, sending it* hanstoria deep into the ti 

 and drawing nil it* nourishment from them ; it liears 

 no green leaves, but only flowers, while the part in 



the ground dies. In the llafllesiare.-i-, a foreign 

 .I. t, remarkable for the si/c of the Mowers of Borne 

 of it* genera, the degradation has gone still further, 

 and the whole plant consists of haustoria, a knob- 

 like ina* of tissue half formexl by the ho>t, and 

 the (lowers. There are some pantiles which un- 

 attached to the root* instead of the stems of their 

 U e.g. Yellow Kattlc. Cow wheat, Kyebright. 

 The attachment by the hau-tori.-t is always remark- 

 ably intimate ; their tissues are always joined to the 

 ponding ones of the host, often in such a way 

 that it is dillicult to say to which plant they belong. 

 The ovules of many parasites are rudimentary, the 

 embryo i* small and without chlorophyll ; in cases 

 of advanced parasitism it may even produce no 

 leaves. There are parasitic genera in many orders 

 1 'orallorhixa in the Orchideie, t'uscuta in I'on- 

 volvulacen-, Onibranche in Labial itlone, Monotropa 

 in l'yrolace;e. The Lorantlmeea-, of which is Viscum 

 the "mistletoe, the Bahmophoreie, and the Santa- 

 larea- are families of doubtful atlinity. Nearly 

 all these parasites have a marked preference for a 

 particular species of host, and they are all flower- 

 ing plant*. Rut there are many others; two whole 

 classes, the Bacteria and the Fungi, are either para- 

 sitic or, what is much the same thing, sapropln tic 

 i.e. dependent upon decaying organic matter for 

 food. The Bacteria have animals as their IP^IS, 

 ami cause in them many diseases, the species Wing 

 often recognised by the disea.se. When they 

 saprophytie. they cause fermentation and putre- 

 faction. The Fungi arc many of them a trouble in 

 agriculture, causing corn, hop, and vine mildew, 

 potato disease (see PLANTS, DISKASKS OF), and 

 also salmon disease; others, like the mushroom, 

 are saprophytes. Allied to parasitism is Symbiosis 

 (q.v.), a sort of mutually arranged parasitism for 

 the benefit of lioth parties; as in the case of the 

 Lichens, which consist of Algnj and Fungi in 

 partnership. 

 r.-ir.-n oliiulin. See TOLUIDIN. 



Paray-le-Monial. a town in the French de- 

 partment' of BaOne-et-Loire, 4S miles by rail W. by 

 N. of Macon, celebrated for its chai'd, in which 

 Mary Alacoque (d. 1690) believc.l hcrsilf to have 

 had "a vision of the Saviour, now the object of 

 pilgrimages by the confraternities of the Sacred 

 Heart (q.v.). "Pop. 32(59. 



Pare*. See FATE. 



Parrliim. a town of Mecklenburg-Schwerin, 

 23 miles SE. of Schwerin. Pop. 1'7'Jii. 



Parchment ( Fr. parchemiii, I.at. jtcnjamrna, 

 through (Jr. from Pfrr/amtis). At a very early 

 period the skins of animals were used for writing 

 upon. Some authors who have written on the 

 subject of ancient writing materials think that 

 the king of Pergamos brought the art of making 

 parchment topeitection through i'tolemy Epipbanei 

 having prohibited the exportation of papyrus from 

 Kgypt. The Romans appear to have written chiellv 

 on papyrus, and this practice was continued in Italy 

 till about the 10th century, but parchment was nl .1 

 used ; and from that time till ordinary paper 1 

 came available in the 14th century paichment was 

 almost the only material employed (see PALEO- 

 GRAPHY, PAPKR). To a limited extent wax tablets 

 and leaden plate* were written upon as late as the 

 14th and 1.1th centuries, and some of these are 

 preserved at Florence. Some of the earliest printed 

 iMxiks were done on vellum (a name originally 

 given to a parchment made of calf-skin), and 

 on a specially fine quality of this substance, iiiadu 

 from tne skins of calves prematurely born, some 

 of the best of the early miniature portniti were 

 painted. Ordinary parchment is chiefly made of 

 sheep-skins, but those of calves and goats are 



