G. H. F. Nuttall 
381 
that she was likewise heavily infested with P. humanus capitis and 
corporis, therefore, it appears to me that the melanism may have been 
due partly or entirely to the latter. There is no doubt that melanism 
may arise in the course of phthiriasis as it does in pediculosis, using these 
terms in their strict sense. There is nothing specific about the melanism 
in either case. When itching, due to the presence of ecto-parasites, is 
maintained, it is the scratching that largely leads to the hyperaemia, 
pigmentation and desquamation. I regret that I have been unable to 
gain access to the papers by Fabre (1902, vide Bibliography) who appears 
to have made a special study of the melanodermia due to lice. 
Summary and Conclusions. 
Phthirus pubis is not known to serve as a vector of any infective 
disease. 
The pathological effects of its parasitism on man are on the whole 
of slight degree. Some persons are more sensitive than others to its 
presence; on the one hand the louse may produce no reaction by its 
bite or it may be tolerated upon the person for years, on the other hand 
it may induce pruritus of a more or less severe character, especially in 
parts of the body that are most infested and where the skin is most 
delicate, i.e. about the genitalia, the axillae, and eyelids. All grades of 
pruritus are observable, scratching of which the individual is unconscious 
may occur, or in the severest cases the scratching goes on day and night, 
so that by day it may be evident to spectators and aid in diagnosis. 
The scratching may only begin from the moment when a person realizes 
that he is infested. 
The pale bluish-grey maculae are a specific sign of the presence of 
Phthirus upon man, but they are not always present. They are induced 
by the adult louse, are few in number, painless, deep seated, do not 
disappear on pressure, and measure 0-2-3 cm. in diameter. The maculae 
mark the site of the insect’s bite; they appear 8-24 hours after the louse 
commences to feed on the spot affected. The bites of P. humanus do 
not produce maculae caeruleae. The salivary glands of Phthirus and 
Pediculus give correspondingly positive and negative results when 
inocidated subcutaneously. The maculae disappear usually within a 
week after the removal of the offending parasite, and they disappear 
more rapidly when the skin is irritated. The nature of the maculae 
remains to be determined, they may be due to extravasated and altered 
blood. 
