14 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



transmission of the European and Indian relapsing fevers, 

 but that lice and not bugs, as first thought, are the trans- 

 mitting agent appears fairly certain. 



Plague. 



Is a disease by no means exclusively tropical. It is a 

 disease of which one of the chief signs is the great swelling 

 of the glands, and hence the term Bubonic plague. The 

 disease is a septicaemia, that is a blood poisoning in which 

 the plague bacilli exist in the blood. Now it has long been 

 known that the outbreak of plague in a place or district is 

 preceded by a mortality among the rats — in fact the rats are 

 dying of plague. We have then to consider the rat factor. 

 Further, it has now been proved that the disease is transmitted 

 from rat to man by means of a particular rat flea, viz., Pulex 

 cheojtis. How does this come about ? In India we have 

 two rats which are important in this connection, viz., Mus , 

 decumanus, the ordinary brown sewer rat, and Mus rattus, 

 the black or house rat. Now it is found in India that 

 the course of plague is the following. Firstly, there is an 

 epizootic among Mus decumanus, i.e., the rat mortality as 

 shown by the dead rats collected is going rapidly up, say in July. 

 It reaches a maximum ; ten days later there is an epizootic 

 among Mus rattus, and then ten to fourteen days later the 

 plague epidemic in man starts. The relationship of plague 

 in man is thus more close in the case of Mus rattus than it 

 is in the case of Mus decumanus. This association of plague 

 with M . rattus is shown by the following curious fact. Plague 

 is equally distributed on all floors of a building, so is M . rattus, 

 but M. decumanus does no go beyond the third floor. We next 

 turn to the flea. It has been shown by numerous experiments 

 — the experiments of Russian investigators though overlooked 



