TRANSMISSION OF DISEASES 399 



wounds which they make with the infected contents of their 

 bodies when crushed. 



Nicolle and his associates also showed that sometimes, at least, 

 the spirochsetes, probably in the granule stage, are hereditarily 

 transmitted through the eggs to the young of the next generation, 

 as is the case with the African relapsing fever parasites in the 

 tick. Experiments on the transmission of the relapsing fever of 

 Algeria with other parasites such as bedbugs, fleas, biting flies 

 and ticks were negative. Some observers, however, believe that 

 in Europe other insects also, notably bedbugs, may be instru- 

 mental in transmitting relapsing fever. The evidence furnished 

 by the epidemiology of the disease is, however, very strongly in 

 favor of iice as the normal transmitters. The Indian form of 

 relapsing fever is also probably transmitted by lice. Further 

 details of the development of the spirochsetes in the lice are 

 given in Chapter IV, p. 44. 



Being transmitted by lice, relapsing fever shows the same pe- 

 culiarities of occurrence as does typhus; epidemics always rage 

 fiercest in winter, and usually break out during war times. Ser- 

 bia, which was so stricken by typhus, was held in the grip of an 

 epidemic of relapsing fever earlier in the war. 



The demonstration of the relation of lice to the transmission 

 of trench fever in 1918 by American and British Commissions 

 working under war conditions was a very brilliant piece of medical 

 research carried out successfully in spite of adverse conditions. 

 For the two years preceeding the beginning of the investigation 

 concerning the transmission of the disease, trench fever is said 

 to have occasioned more sickness among the troops in France 

 than any other infectious disease. The work of the Commissions 

 showed that trench fever is naturally transmitted by the body 

 louse, and that this is the important and common means of trans- 

 mission. The louse may transmit the disease by its bite alone, 

 or by infection of abraded sink by the excrement. A discussion 

 of Rickettsia quintana, the probable cause of trench fever, and its / 

 occurrence in infected lice will be found on p. 187. 



Lice may also serve as mechanical transmitters of still other 

 diseases. The bacilli of bubonic plague have been found alive 

 in both body lice and head lice taken from victims of the disease, 

 and both this species and the body louse have been experimen- 

 tally proved to be able to transmit plague from rodent to rodent 

 in Java. De Raadt in Java infected rodents with plague by in- 



