50 SUMMAEY OF CURKENT RESEARCHES RELATING TO 



virus occurs tlirough the bite of infective lice, or through such lice bein^ 

 crushed upon the skin when it is scratched. liice remain infective for 

 at least eleven days. Lice are invariably present in connexion with 

 typhus outbreaks. The destruction of lice upon a typhus patient renders- 

 him innocuous. The prophylaxis of typhus consists in louse destruction. 

 Bed-bugs and fleas do not convey the disease. 



Epidemiological evidence, as in the case of typhus, points to relapsing 

 fever being louse-transmitted. The microbe {Spiroch'deta recur rentis} 

 passes from parent louse to its offspring. As Nicolle and others have 

 shown, lice do not convey relapsing fever by their bites. Infection 

 occurs through the lice being crushed on the skin, or infective material 

 may be carried on the fingers to nose or eye. The spirochaHecan invade 

 the system through intact mucous membranes. The author discusses 

 miscellaneous infective diseases which lice may spread, and the primary 

 effects of biting. The secretion of the salivary glands has some degree 

 of toxicity. The secretions of the two sets of salivary glands contain^ 

 Nuttall found, a substance which retards the coagulation of the blood. 



Biology of Lice.*— G. H. F. Nuttall has gathered together the 

 observations which have been made on the life and "habits of 

 Pedmilus humanus, adding here and there his own. The species is 

 restricted to man, its nearest relative occurring on monkeys. It lives 

 solely on blood, for sucking which the mouth-parts are adapted. 

 After the nit or egg-stage, there are three larval stages and the adult ; 

 from the first larval stage to the adult there are three moults. The 

 single sharp claw on each leg is suited for progression on hair. Body- 

 lice {P. corporis, P. vestmenii) and head-lice (P. capitis) are at most 

 merely racial forms of Pediculus humanus Linnaeus. The distribution 

 appears to be world-wide, but there is some dearth of precise data. 



In modern times lousiness is largely confined to the poorer classes 

 and to soldiers in the field. It seems that capitis occurs more fre- 

 quently on females than on males, and that the reverse holds to a 

 certain extent for corporis ; there is a greater prevalence of capitis in 

 children and old people. There may be over 10,000 lice of corporis 

 about one person and over 1,000 of adult and larval capitis ; there 

 appears to be an increase in winter and a decrease in summer. Man 

 becomes infested by contact with verminous healthy people ; by contact 

 with infected sick, dying, and dead ; by contact with infested clothing, 

 bedding, brushes ; and by stray lice. Lice may be casually carried by 

 wind and by flies. 



The rate of locomotion varies with temperature, illumination, and 

 the nature of the surface. Nuttall observed on sateen a rate of 1 

 metre in 2 minutes 43 seconds ; on hair 20 cm. in 1 minute 24 seconds 

 to 3 minutes 10 seconds, or more. Lice can cover in a few minutes a 

 distance equal to the length of a man's body. 



The second part of NuttalFs paper gives an account of the methods 

 of raising lice experimentally — notably the felt-cell method and the 

 wristlet method — and some other practical points. With a questionable 



* Parasitology, x, (1917) pp. 80-185 (2 pis. and 12 figs,). 



