The parasites of man, and the diseases which proceed from them : a text-book for students and practitioners / by Rudolf Leuckart ; translated from the German, with the co-operation of the author, by William E. Hoyle.

Date:
1886
Catalogue details

Licence: Public Domain Mark

Credit: The parasites of man, and the diseases which proceed from them : a text-book for students and practitioners / by Rudolf Leuckart ; translated from the German, with the co-operation of the author, by William E. Hoyle. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    42/808 (page 10)
    OCCURRENCE OF PARASITES. J ust as there is hardly a single creature which is not preyed upon by some carnivorous foe, so it seems probable that every animal gives shelter at one time or another to some parasite. We are even acquainted with cases where the parasite itself is subject to the attacks of other parasites. Many of the parasitic Crustacea, for example, give shelter to mites or thread-worms; the parasitic larva of the ichneumon-fly again is inhabited by other minute parasitic larvae (Pteromalinse.) In the case of the Nematode, Tricliosomum crassicaiida, which infests the rat, we find three or four males living parasitically within the uterus of the female.1 Neither small dimen- sions nor a concealed mode of life offer the slightest protection against these enemies. Nevertheless, every animal is by no means equally subject to the attacks of parasites; on the contrary, we find the greatest differences in this respect. In certain animals, the presence of parasites appears to be the rule, since they may be found in great abundance2 in every individual examined; in certain others hundreds of specimens may be searched without finding a single parasite. On the whole, it may be safely stated that the Vertebrata are far more generally infested by parasites than the Invertebrata, and indeed it was thought for a long time that their occurrence in the latter was a mere accident. Which- 1 See Vol. II. The recent researches of Biitschli and von Linstow have fully de- monstrated this fact. Moreover, there is another free-living worm {BoneUia), the male of which in a Bimilar fashion lives within the genital duct of its own female. See Kowalewsky, Du male planariforme de la BoneUia, Revue des Sci. Nat., pL iv., 1875 (translated from the Eussian); Vejdovsky, Zeitschr. f. wise. Zool., Bd. xxx., p. 487, 1878 ; Spengel, Mitthcil. zool. Stat. Ncapel, Bd. i., p. 357 et scq. 2 The snipe, the goose—so long as it lives in meadows—the turbot, have their intestines almost always filled with numerous Helminths, generally Cestodes. How vast is occasionally the number of parasites is shown by certain cases of trichinosis and the Cochin-China diarrhoea. Even the larger intestinal worms are sometimes found in great numbers. Bloch ( Abhandlung von der Erzeugungder Eingeweidewlirmer, Berlin, 1782, p 12) found in a male bustard at least a thousand specimens of Tccnia viUosa, some of which were no less than 4 feet in length. Gbze also ( Versuch einer Naturgeschichte der EingeweidewUrmer, 1782, p. 32, note) found the alimentary canal of a parrot so full of Cestodes, 20 ells in length and about the thickness of a straw, that it (intestine) was almost ready to burst. When the whole mass was placed in water, Goze was astonished