RESEARCHES ON ACARIDS AMONG LEPERS. 465 



My personal investigations, although not conducted systematically 

 enough to furnish a very definite conclusion, indicate that, exclusive of 

 children, Demodex does not live on more than one-quarter of the' indi- 

 viduals who are in health. 



I believe that the apparently great differences existing between these 

 various statistics, for instance, between Gruby's report of 66 Megnin's 

 of 10 per cent, are due to slight errors which have not sufficiently been 

 taken into account. I pointed out one of these when indicating the 

 preferable technique which will make such an investigation fairly 

 successful. 



However, an important fact, admitted by all observers, and one which 

 does not agree with Borrel's theory, is that young children never 

 are the hosts of Demodex. Now, many cases of children attacked by 

 leprosy have been noticed ; according to Sauton the disease often manifests 

 itself in them at the early age of 4 or 5 years. 8 



It may be interesting here to report some observations on the kinds 

 of sebaceous glands inhabited by Demodex. In this connection, we 

 must distinguish between normal sebaceous glands and obstructed ones 

 which give birth to comedones (blackheads) and to the different varieties 

 of acne. The parasite often lives in perfectly normal glands. 



Comedones (blackheads) are formed in glands the openings of which have 

 been obstructed, and as the glands continue to secrete, they sometimes swell by 

 the accumulation of their own products. The plug is formed by a portion of 

 sebum which has hardened in the same way that the majority of vegetable and 

 animal oils thicken by contact with the air, that is, by oxidation. The formation 

 of this plug is assisted by dust which adheres to the surface of the sebum. This 

 explains the more frequent existence of comedones on persons who are careless in 

 personal cleanliness. However, want of cleanliness is not the principal cause of 

 comedones; they are influenced chiefly by personal predisposition, either because 

 the sebum of certain individuals is naturally thicker, because dust sticks to it 

 .more readily, or because it contains substances which tend to harden more rapidly 

 by oxidation. For instance, one meets people of the upper classes who are ex- 

 ceedingly careful in their personal habits, but who suffer great annoyance, from 

 comedones and on whom they persistently reappear in spite of every care. On 

 the contrary, there are workmen and beggars who certainly do not wash every 

 day who have no comedones. I may also add, that persons subject to fatty 

 seborrhoea, not too intense, provided they wash the face with care, often have no 

 comedones in spite of the abundance of sebum; this is probably because the latter 

 is soft and rapidly evacuated. 



I mention these well-known and apparently insignificant details to 

 show that Demodex may wrongly have been designated as the cause of 

 comedones. Besides, and this brings us back to our subject, in studying 

 the content of some hundreds of sebaceous glands, I found Demodex 

 much oftener in normal ones, 'with open orifices, than in comedones. 

 Balzer had already noted the same thing. This might have been expected 



"Sauton. La Leprose (1901), 327. 



