472 LEFEBVRE. 



easily be explained if the acarid, bearer of the contagion, were migratory; 

 it can not be explained if it is fixed. Besides, how should Demodex 

 carry the contagion from one person to another ? 



Borrel states that the conditions of migration of Demodex are un- 

 known. 14 It is true we have not as yet a complete account of its life 

 history, but the few facts which seem well established are sufficient to 

 show that Demodex folliculorum stays at home. No observer has met 

 with it outside the sebaceous glands. For my part, I have often examined 

 the scrapings of the skin near the glands containing Demodex; and I 

 did so periodically in the particular case of an individual infected with 

 the parasite, but with negative results. 



Moreover, the anatomy of Demodex renders, it unfit for the work; 

 its legs, consisting of only three very short articulations instead of five as 

 with the migratory acarids, such as Sarcoptes scabiei. are exceedingly 

 small; they resemble little conical tubercles and it seems hardly possible 

 that they could carry the animal's enormous abdomen. In fact, when 

 Demodex is observed under the microscope, it is very easy to see the 

 difficulty it experiences in moving even a few tenths of a millimeter, and 

 this difficulty is increased by the mass of sebum in which it is embedded. 

 Therefore, the individuals of Demodex are prisoners, so to say, in the 

 sebaceous gland in which they have been developed, living normally in 

 the lowest parts, with the head generally turned to the bottom. Their 

 reproduction takes place in their prison. Nathan Banks thinks that, if the 

 Demodex lays eggs, they must be fusiform, 15 but I think he is mistaken. 

 I have never met. with true eggs of the parasite; one must probably admit 

 with Megnin 1C that what have been taken for eggs really are apode 

 larva?. As these develop, .they acquire six little unarticulated papilla? 

 which represent the legs, and then, by successive moults, the eight pairs of 

 articulated legs of the adult. 



These larva? are carried out of the gland with the mass of sebum as it 

 escapes, little by little, and they alone could transport the contagion of 

 leprosy, but only in the same way as the sebum itself, and the residue 

 of the cells and other particles that it contains could do the same thing. 

 Evidently the sebum, the particles, and the Demodex larva? may be covered 

 with the Hansen bacilli and mav disseminate them ; but this would result 

 only in a passive contagion. The idea then must be abandoned that 

 Demodex is an active propagator of leprosy, as, for example, is, in some 

 diseases, the mosquito or glossina which has sucked the virus of a patient 

 and which then inoculates another individual by stinging him. 



I have often looked for the Hansen bacillus in the body of Demodex, 

 but without success; I can not say that it never penetrates the body, for 



" Hid. 



15 A Treatise on the Acarina or Mites, Proc. U. 8. Nat., Mus. (1905), 28, 1. 



16 hoc. cit. 



