PARASITES. 



[ 578 ] 



PARASITES. 



eluded a uumber of microscopic animals 

 and plants infesting other animals and 

 plants, and often nourished at the expense 

 of their structures or juices. Almost eveiy 

 animal and plant is subject to parasites, 

 both in the young and the adult state ; and 

 in some instances, the parasites are them- 

 selves infested by other parasites. The 

 parasite may live on the surface of the 

 parasitiphore or host, or within its tissues 

 and in the cavities of its organs ; hence the 

 division of parasitic animals into epizoa 

 and entozoa. The commonest parasites 

 either feed upon the deca;y'ing external 

 skin -tissues, or are nourished at the expense 

 of the blood and fluids. In some remark- 

 able instances, as in the cirripeds, the male 

 appears to live parasitically upon the fe- I 

 male ; and in almost every case of para- ' 

 sitism there is a complicated life-cycle, often 

 accompanied by strange adaptations and 

 degenerations of form, so that often the 

 parasite ultimately resembles but slightly its 

 free and primitive form. Of the Animal 

 Parasites, many are not microscopic, but 

 the following sketch may be useful for 

 reference. The chief portion belong to : — 

 The Crustacea, Order Siphonostoma, as 

 Caligus, Cecrops, Lcemargus, Nicotho'e. The 

 Aeachnida, Ord. Acariua, as Sarcoptes, 

 the itch-insect ; the Ixodea, or ticks ; the 

 Gamasea, on insects ; Tromhidium, the 

 harvest-bug; the Hypoderidee, in birds; 

 the Phytoptidse, in galls. The Insects, 

 especially the Anoplura, as Htsmato^nnus, 

 Pediculus (the louse), and Phthirius ; Pedi- 

 cimis ; and TricJiodectes. The Entozoa, 

 as Tcenia {Ccenunis, Cysticercus, Echino- 

 coccus) ; Distoma, in the hver; Bilharzia, 

 in the human blood-vessels, the ova in the 

 lU'iiie in endemic hsematuria and chyluria ; 

 the Nematodes, Anyuilhda intest. and ster- 

 coralis, and TJocJimius, in tropical diarrlicea ; 

 Sderostoma synfjamiis in poultry, producing 

 the " gapes;" Stromjylns 2}eryrucilis in the 

 Grouse-disease. The Infusoria, Oj)alma, 

 Trichomoyuis, &c. ; and the Gregabinida, 

 Psorospermice in mammals, and insects 

 (Pebrine). 



These are described under the respective 

 heads. 



The Plants parasitic on animals chiefly 

 belong to the class of Fungi, and are tole- 

 rably numerous ; but many of the forms 

 which have been described are certainlj" 

 not distinct plants. They will be most con- 

 veniently emmierated under the heads of 

 the classes of animals infested. 



Man and Mammalia. 



On the Skin. — Achorion Schcenleinii and 

 Puccinia favus, on the hair and in the 

 follicles, in favus. Trichophyton ton- 

 siiranSf on the hair in plica polonica and 

 favus ; this appears to be a Tonda-like 

 growth, probably not a mature plant. Tr.? 

 spondoides, Rob., occurs in plica ; and Tr.? 

 ulcerina, Rob., in the pus of ulcers. Micro- 

 sporon Audouinii occurs in the hair-fol- 

 licles in porrigo decalvans : M. metdagro- 

 phytes. on the beard &c. ; M. fiirfiir, on the 

 skin of the chest tS:e. in pitja-iasis versicolor. 

 The occurrence of 3Iuco)- mucedo on the 

 skin, and of an Asj^ergillus in the external 

 conduit of the ear, must be regarded as 

 accidental. 



On tlie mucous surfaces or in cavities. — 

 Sarcina ventricidi in the stomach ; Torula 

 cerevisice (?), ditto. Various species of 

 Leptomitus, which must be regarded as 

 imperfect mycelial growths, found in almost 

 all the cavities of the body. Oidium albi- 

 cans, the fimgus of aphtha, probably a pe- 

 culiar condition of PENicii,LirM;'ie/;;'o- 

 tlirix hiccalis, a filamentous growtli constant 

 between the teeth, probably some allied 

 mycelium. 



Birds. 



Various species of Aspergillus have 

 been found in the kmgs and air-sacs ; their 

 introduction would appear to be accidental. 

 In the eggs of the common fowl, Dacty- 

 LiuM ooyenum occurs not imfrequeutly, 

 sometimes on the membrane of the yolk, 

 sometimes on the outer membrane, just 

 beneath the shell. — Sporotrichum hrun- 

 neunt, Schenk, in the white of eggs, convert- 

 ing it into a brownish gelatinous mass. 



Iteptiles and Fishes. 

 On the skin of Tritons, as of Fishes, 

 Achlya {Saproleynia) is frequently ex- 

 tremely developed ; other obscure forms are 

 also enumerated by Robin. The same author 

 describes the Psorospeemi^ as Algfe allied 

 to the Diatomacea; ; but they are pseudo- 

 navicidaj of Gregarina. 



Berkeley has recorded the occurrence in 

 Denbighshire, on the scales of goldfish, of a 

 '\ lichen identical A^dth one wliich is found on 

 stones in neighbouring streams. 



Insects 



are subject to the invasion of various para- 

 sitic fungi, among the most remarkable of 



