RESEARCHES ON ACARIDS AMONG LEPERS. 471 



or less explain the only fact which seems to favor the theory of infection 

 through the sebaceous glands : namely, the parts where the first manifes- 

 tations of leprosy are found are the sides of the nose and ears. However, 

 it must be acknowledged that this hypothesis is purely without founda- 

 tion. I suggest it, because in doubtful questions no possible hypothesis 

 should be neglected. Comil and Babes in 1888 thought that the integu- 

 ment, the sebaceous glands, and the follicles of the hairs in particular 

 are a means, not only of elimination, but probably of the ]Denetration of 

 the bacilli also. 



Whether this theory is true or not, I think I may conclude from all 

 that precedes, that (1) it is difficult to reconcile the observed facts with 

 the hypothesis that Demodex folliculorum is the principal agent of leprous 

 contagion; and (2), that no positive argument can be drawn from the 

 existence of external leprous lesions to prove that contagion takes place 

 by way of the skin. 



II. 



So far we have considered Borrel's theory of the contagion of leprosy 

 by acarids more particularly with regard to the place where the bacilli 

 might be introduced and where they might multiply. It remains for 

 us to consider the agent itself, which Borrel supposes to be the bearer of 

 the contagion, and to ask if it possesses the qualifications necessary for 

 this function. 



The genus Demodex, the only one of the family Demodecida, comprises 

 only one species, Demodex folliculorum Simon, which is divided into 

 several vareties, of which only one appears to live in the human skin, the 

 var. hominis Simon. 



Besides Demodex, the acarian parasites of the human skin thus far 

 encountered are the following: Sarcoptcs scabiei Latr., parasite of the 

 itch, Sarcoptes of the Norwegian itch, the identification of which is 

 'uncertain and which perhaps is only a variety of Trombidium holosericum 

 Herm. ; various species of Ixodes and Argas. There are probably some 

 other acarian parasites of man as yet but little understood. Demodex is 

 the only fixed acarian parasite known to live in the human skin ; the 

 others cited are all more or less migratory. 



Borrel states as follows: "Lepers must be infected by Demodex or 

 other fixed acarids. I found it impossible to determine on the sections, 

 the species or variety of the parasites I saw." 13 Wiry should the suspected 

 parasite be fixed? Is not a migratory acarid more to be feared? It is 

 precisely this sedentary character of Demodex folliculorum which seems 

 to me to afford the best argument against Borrel's theory. We have 

 seen that one often meets with areas of the skin quite recently attacked 

 by leprosy, the follicles of which contain no Demodex; this fact would 



13 Ann. Inst. Past. (1909), 23, 127. 

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