CHAPTER XVIII 



THE RISE AND FALL OF DISEASE. — PLAGUE, TICK 

 FEVER, LEPllOSY AND TUBERCLE 



RELAPSING FEVER {SPIRILLOSIS) AND PLAGUE 



Plague. — The term " vermin fevers " might not 

 inappropriately be given to the two diseases known 

 respectively as relapsing fever and jj /ague — two diseases 

 as widely distributed over the globe as the vermin 

 which have been proved to take a large share in their 

 transmission. In their very wide distribution over the 

 temperate and tropical zones they differ from yellow 

 fever, malaria, and sleeping sickness, the insect carriers 

 of which diseases flourish more vigorously in warm 

 climates. 



It is therefore not surprising that both these 

 fevers have a world-wide distribution, as world-wide 

 as the crawling and lively insects associated with 

 them, namely, ticks and possibly bugs in the case 

 of relapsing fever, and fleas in the case of plague. 

 Nor is it surprising to find that both these diseases 

 are being confined to diminishing areas of the globe. 

 Time was when probably both had a far wider dis- 

 tribution than they have to-day. We know that 



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