70 
Lice and Disease 
amount of irritation produced. In 48 cases the lice were found upon 
the clothing, in 16 cases upon the head and clothing. The Editorial 
also refers some cases of urticaria and most cases of porrigo of young 
persons’ heads to the presence of lice and suggests the name “Pedi- 
cularia” for diseases caused by lice. 
It is difficult to know how much to attribute to the primary effects 
of lice and how much to secondary effects due to a number of different 
causes. Head-lice may produce urticaria, eczema and pustular derma¬ 
titis, the first two of these being probably primary effects due to the 
lice themselves and their secretions. In the previous section, refer¬ 
ence was made to a condition which Salomon (1912) was inclined to 
attribute to the primary effects of lice that have been crushed upon 
the skin of the fingers and head. 
Peacock (1916, p. 44) refers to “louse rash’’ as being distressingly 
common among the British troops. 
Plica polonica. As a result of the eczema or pustular dermatitis 
accompanying the presence of lice upon the scalp, the exudation from 
the skin leads to the formation of scabs and crusts, especially about 
the nape of the neck. In bad cases that are neglected the condition 
known as plica polonica may supervene; wherein the hair, scabs and 
crusts become matted together in a solid mass at the back of the head. 
The name plica polonica had its origin from the condition having been 
frequently observed among the poor Jewish population of Poland. 
V. PRIMARY EFFECTS OF LOUSE-INFESTATION. 
In persons who are infested by lice, the presence of the insects is 
at once indicated by the reaction which usually takes place about 
the seat of the bite. The bites produce minute haemorrhagic spots 
that are chiefly disseminated over the neck, back and abdomen. 
These spots are accompanied by more or less urticaria, the itching 
leading to scratching so that the skin appears scored in a linear manner 
by the fingers. In tramps, chronic drunkards and vagabonds who 
may harbour lice for years, the skin over the most frequently bitten 
areas becomes rough, thickened and deeply pigmented, the condition 
being known as morbus errorum or vagabonds’ disease. Pediculosis 
alone may at times produce fever, which has been attributed to the 
cutaneous irritation and possibly to the toxic action of numerous 
louse-bites. 
The melanodermia or skin pigmentation above mentioned, in marked 
