PARASITIC DISEASES constitute one of the recognized orders of disease in Dr. Farr's classification. See NOSOLOGY. In these diseases, certain morbid conditions are induced by the presence of animals or vegetables which have found a place of subsistence within sonic tissue or organ, or upon some surface of the body of man or of other animals. Even plants are not exempt from disorders of this nature (see PARASITIC PLANTS). The forms of animal life giving rise to parasitic diseases are described in articles ASCARIDES, CV:STOW-WORMS, ENTOZOA, EPIZOA, GUINEA-WORM, ITCH-INSECT, LOUSE, NEMATELMIA, STRONGVI.L7S, TAPEWORMS, TRICHINA, etc.. With the vegetable structures which give rise to special diseases we arc less accurately acquainted, in consequence of the limited knowledge of eryptogamie botany possessed by many writers who have recorded their experience of these cases. These parasites are either fungi or alga•, and are composed of simple sporules, germs, or cells, or of cells arranged in rows, or groups, which are so minute as to require the microscope for their recognition. Fungi are the most ninner oils of all plants iu regard to genera and species, and their growth is associated with serious injury both to animal and vegetal)] • life. It is not, however, always easy to whether they are the direct cause of disease, or whether the diseased 'tissue has merely afforded a suitable nidus for their development. "It is certain," says Dr. Ait ken, who has entered more fully into this subject than .any other English writer on the practice of medicine, " that wherever the normal chemical processes of nutrition are impaired, and the incessant changes between solids and fluids slacken, then, if the part can furnish a proper soil, the crvptogamie parasites will appear. The soil they select is, for the most part, compbsed of epithelium or cuticle, acid mucus or exudation. Acidity, however, though favorable to their growth, is not indispensable, since some of the vegetable parasites grow upon alkaline or neutral ground, as on ulcerations of the trachea, or in fluid in the ventricles of the brain. Certain atmospheric conditions seem favorable to the occurrence of these vegetable parasites. For example, tiara tousurans may be quite absent for years in places such as work-honses, where it commonly exists, and then for several months every second or third child in the place gets the disease." There is undoubted evidence from the observations and experiments of Devergie. Von 13Eirensprung, and others, that these parasitic diseases may be transmitted by contagion from horses, oxen, and other animals to man; while conversely, Dr. Fox an instance of a white cat which contracted the mange from tinea tonsurans (ringworm of the scalp), which affected the children of the family to which it belonged—the fungus of the mange in the cat being the same fungus as that of tiara in the human subject, viz., the tricophyton (Gr. tric (file), of a hair, and phyton, a plant).
The principal vegetable parasites associated in man with special morbid states are arranged by Aitken (The Science and Practice of Medicine, 1863. 2d edit., vol. ii.. p. 171) as follows: 1. The trycophyton tonsurans, which is present in the three varieties of tiara tondens—viz., T. circuirthis (ringworm of the body), T. tonsurans (ringworm of the scalp),
and 1. sycost:s month (ringworm of the heard). 2. The tricophyton sporuloides, which, together with the above, is present in the disease known as plies polonira. 3. The achorion sdaialeinii, and puccinto fart, which are present in T. farosa, known also as farms (q.v.), and porrtYo scutulata (the honeycomb ringworm). 4. The microsporon mentag•o phyla, which is present iu meHfagrrt. 5. The microsporon fuifu•, wide]) occurs in pityriasis versuolo•. 6. The mic•osporon audonini, which is present in po•riyo *entrails. 7. The mycetoma or chionyphe carteri, which gives rise to the disease known as the " fun gus foot of India," etc. 8. The oidzum albica ns of diphtheria and aphtlia. 0. The rryp tococcus cerevishr, or yeast plant, occurring in the urine and contents of the stomach, if there is saccharine fermentation. 10. The sa•eina yoodserii, or merispaylia rentrienli (of Robin), found in vomited matters and in the urine. There are strong grounds, based partly on botanical and partly on clinical observation, for believing that the various fungi already described are mere varieties of two or more species in various phases of development.
We shall conclude this article with a briU notice of the most dangerous of all the parasitic diseases—the fungus foot or fungous disease of India. It occurs in many parts of India, and the n.e. shores of the Persian gulf. It is a disease which occurs among natives only, so far as has been yet observed, and is undoubtedly due to the presence of a fungus which eats its way into the bones of the foot and the lower ends of the tibia and fibula, penetrating by numerous fistulous canals through the tissue of the entire foot, and tending to cause death by exhaustion, unless amputation is performed in due time. Dr. Carter has described three forms of this disease, in which both the symptoms and the fungoid material differ considerably from each other. A few remarks on the first of these forms will suffice as an illustration of parasitic disease. In this form the bones of the foot and the lower ends of the leg-bones are perforated in every direction with round ish cavities, varying in size from that of a pea to that of a pistol-bullet, the cavities being tilled with the fungoid matter. The surrounding muscles, and subsequently the tendinous and faux structures, are converted into a gelatiniform mass, in consequence of which the foot presents a peculiar turgid appearance. Examined under the micro scope, the fungoid mass is found to consist of short, beaded, tawny threads or filaments, arising from a common center, and having at their tips large spore-like cells. For fur ther information regarding this remarkable forth of disease, the reader is referred to Dr. Carter's paper in the fifth volume (new series) of the Transactions of the ..1Icdical and Phy sical Society of Bonibay,.and to the rev. M. J. Berkeley's account of his examination of the fungus, in the second volume of The Intclkctual Obserher, p. 248.
Further notice of the parasitic diseases of the skin will be found in the articles PITY IiIASIS /Tie/CO(00, RINGWORM, SCALD-IIEAD, etc.