78 
Lice and Disease 
Miscellaneous infective diseases which lice may spread. 
It is reasonable to. suppose that plague may occasionally be con¬ 
veyed through the agency of infected lice that are crushed upon the 
person, the bacilli, recently ingested by the insects, entering through 
the excoriated skin. 
Mycotic or pyogenic infections like favus, pityriasis, impetigo con¬ 
tagiosa, furunculosis and more generalized suppurative processes, may 
be spread by lice acting as mechanical carriers, the microorganisms 
perhaps merely clinging with the aid of pathological exudations to the 
outer surface of the insects. The irritation and consequent scratching 
induced by lice lead to the dissemination of the disease agents upon 
the person, the latter spreading the infection by auto-inoculation of 
the excoriated skin. 
Various pathological conditions, other than those above mentioned, 
are cited as being attributed to the presence of lice; a number of these 
are referable to secondary infective agents, coupled with the general 
lowering of the infested individual’s vitality induced by pediculosis. 
Primary effects of infestation with lice. 
In biting, as I have found by tests upon my arm, the louse produces 
a slight transitory pricking sensation or no sensation whatever; it is 
only after an appreciable interval that the seat of the bite begins to 
itch, this being after the louse has left. The reaction at the seat of 
the bite varies considerably in degree, it may be so slight as to be 
negligible or it may cause much itching. In the first case a minute 
congested spot is visible at the point bitten ; the redness about the 
puncture may vanish in about half-an-hour or it may persist longer. 
In the second case a variable degree of oedematous swelling surrounds 
the puncture and forms a papule accompanied by pruritus. When 
bites are repeatedly inflicted on the same spot the papules coalesce, 
the skin becomes roughened, reddened, thickened, and more or less 
pigmented. The effect of the bites of individual lice varies even when 
they are allowed to feed without interruption. The amount of reaction 
following louse-bite varies in different persons. As the result of being 
frequently bitten, some persons acquire immunity to the effects of the 
salivary secretion of the louse, the secretion having, as evidenced by 
the reaction, some degree of toxicity. I have found that the secretions 
of the two sets of salivary glands of the louse (the reniform and con- 
