LUPUS 505 



for some time after it, and should it break out again several weeks 01 

 months after the treatment has been suspended, the same procedure 

 must be repeated. 



Among the external applications which have been employed for 

 the purpose of modifying the nutritive state of the skin, and to pre- 

 vent the recurrence of the eruption, are the ointments of the iodides of 

 mercury, sulphur, and potassium. 2 



VII. PARASITES IN THE SKIN. 



THE development of microscopic fungi is a constant accompani- 

 ment of certain diseases of the skin ; in others, again, they are some- 

 times present, while as a general rule they are absent. Favus^ pity- 

 riasis versicolor, and herpes tondens belong to the former class. The 

 constant presence of fungi in these diseases, and their contagiousness 

 by transfer of the fungi from one individual to another, is our sole proof 

 that the generation of such fungi is the primary and essential lesion 

 of the diseases. As the fungi are always found, and as transmission 

 of the disease by transfer of the fungi always succeeds, no doubt can 

 be entertained of the parasitic nature of these affections. To our 

 description of favus, herpes tondens, and herpes versicolor, we shall 

 add an account of the itch, as the cause of the cutaneous lesions in this 

 disorder is the presence of a parasitic animal. 



The acarus folliculorum is also a very common parasite. It exists 

 in most persons, and may easily be obtained by scraping the nose with 

 the back of a knife. As this animal does not give rise to any disease 

 of the skin or its follicles, of which it seems to be a perfectly harmless 

 inhabitant, it possesses no pathological interest, and we may forego 

 further description of it, and omit the account of the various hypotheses 

 which have been advanced as to its importance as a matter of natural 

 history. 



CHAPTER XIX. 



FAVTTS PORRIGO FAVOSA, LTJPINOSA. 



ETIOLOGY. Schonlein was the first to demonstrate that certain 

 dry, straw-colored crusts, found chiefly upon the hairy scalp, and for- 

 merly called porrigo favosa, or tinea lupinosa, and which were re- 

 garded as the product of a dyscratic pustulous inflammation of the 

 skin, really consisted of a mass of fungous spores and germinal fila- 

 ments (the oidium, or achorion Schonleinii). The spores of favus 



