Ct. H. F. Nutt all 
379 
unwarranted assumption, there being no evidence whatever that the 
bluish spots are caused by the pigment which occurs in the louse’s 
fat-body. 
Huguenay (1902, Gaz. des hop., p. 591, cited by Tieche) believes that 
the saliva of the louse is toxic and that it alters the haemoglobin in 
some way about the seat of the bite. Vignolo-Lutati (1909, pp. 365-378) 
cites Gravagna (no reference) as attributing the pathological effects of 
crab-lice to a toxin, but he does not share this author’s views. In other 
words, the authors above quoted regard the spots as due either to a 
genuine pigmentation (Oppenheim) or to a toxic erythema (Huguenay, 
Gravagna). 
According to Ciuhu {loc.. cit.) an extract of crab-lice is not haemolytic. 
He remarks that the maculae do not go through the series of colour 
changes that bruises do in fading, and therefore concludes that blood 
has nothing to do with the causation of the spots. He found, moreover, 
that the extract of P. humanus does not produce similar maculae. 
Finally Tieche (1908, p. 327) took up the problem experimentally. 
He cut up crab-lice in water or salt solution upon a slide, mixed the 
substance with blood and observed that the blood assumed a violet 
colour after 1-5 minutes in the vicinity of the louse fragments. He 
concluded that this colour change was merely due to the reduction of 
the oxyhaemoglobin by the fresh louse tissues, the violet colour dis¬ 
appearing when he admitted air by lifting the coverglass from the 
preparation. Spectroscopic examination confirmed him in his belief. 
He found that fragments of flies, corporis, or rabbit muscle, produced 
an identical effect when mixed with blood. 
Like other observers, Tieche noted that the maculae disappear if 
the skin is irritated. Phthirus usually does not irritate the skin, whereas 
P. humanus does, whence he explains the absence of maculae in cases 
of infestation with the latter species. Tieche concludes that the maculae 
are probably due to the infiltration of the skin with corpuscular elements 
beneath the epithelial layer, the blood colour being altered. 
