148 



Insects and Disease 



tain plague microbes when the bites have been inflicted 

 from 12 to 26 hours before the death of the animals, 

 that is, during that period of their illness when their 

 blood contains plague bacilli. 



"(3) The vitality and virulence of the plague mi- 

 crobes are preserved in these insects. 



" (4) Plague bacilli may be found in fleas from four 

 to six days after they have sucked the blood of an 

 animal dying with plague. In bugs, not previously 

 starved or starved only for a short time (one to seven 

 days), the plague microbes disappear on the third day; 

 in those that have been starved for four to four and one- 

 half months, after eight or nine days. 



"(5) The numbers of plague microbes in the in- 

 fected fleas and bugs increase during the first few days. 



"(6) The faeces of infected fleas and bugs contain 

 virulent plague microbes as long as they persist in the 

 alimentary canal of these insects. 



"(7) Animals could not be infected by the bites of 

 fleas and bugs which had been infected by animals 

 whose own infection had been occasioned by a culture 

 of small virulence, notwithstanding the fact that the 

 insects may be found to contain abundant plague mi- 

 crobes. 



"(8) Fleas and bugs that have fed upon animals 

 which have been infected by cultures of high virulence 

 convey infection by means of bites, and the more 

 certainly so the more virulent the culture with which 

 the first animal was inoculated. 



