iO 



mice with material obtained from such fleas, but only one of them died, 

 the other two survived. 



Loir goes so far as to see the principal intermediary carrier of plague 

 between rat and man in the flea. But, as Galli-Valerio has pointed out. 

 Loir has really no valid experiments to support his claim, which he 

 sees fit to bring forward as a demonstrated fact. 



Kolle has systematically attempted to infect healthy rats from those 

 sick with or dead of plague through the agency of fleas. However, he 

 has never succeeded in transmitting plague in this manner, though he 

 was able to demonstrate that fleas had really traveled from the sick rats 

 to the healthy ones. From his observations on rats he thinks that the 

 disease spreads among these animals because the living eat the cadavers 

 of the dead of their own kind and not because of fleas which pass from 

 the plague-sick to the healthy individuals. The primary bubo in rats 

 dead of plague is generally found in the submaxillary region, which 

 points to an infection through a slight lesion of the buccal mucosa. Kolle, 

 in speaking on this subject, very properly remarks: "It is clear that 

 plague bacilli will enter the body of parasitic insects which suck the 

 blood of animals sick with the plague. It has, however, not yet been 

 shown beyond doubt that the bite of such parasites w^ill infect other 

 healthy animals." 



Nuttall made experiments to clear up the question as to what part 

 insects play in the spread of plague. He demonstrated that when flies 

 had been fed on material containing plague bacilli they still harbored 

 the virulent organisms twenty-four and even forty-eight hours after the 

 last feeding. According to this author, the danger of a spread of the 

 disease through bedbugs is negligible. The evidence in favor of the "flea 

 hypothesis" as far as the spread of plague is concerned, Nuttall considers 

 worthless and unable to withstand scientific criticism. He states that 

 all of his attempts to infect rats or mice through the bite of freshly infected 

 fleas have proved futile. 



Galli-Valerio severely and justly criticises the evidence so far brought 

 forward to show that rat fleas play the most important part in the 

 dissemination of plague among the human inhabitants of a district 

 infected with this disease. He particularly shows that most of those 

 who, on very insuflicient evidence, assumed tliat fleas from rats spread 

 the plague among human beings, have not even ascertained whether the 

 species of fleas infesting the rats will bite man. Galli-Valerio found 

 Typhlopsylla musculi and Pulex fasciatus on European rats and mice under 

 normal conditions. He allowed himself to be invaded by fasting individuals 

 of these two flea species, but neither of them bit him. By this investigator 

 Pulex serraticeps, the flea infesting dogs and cats and which occasionally 

 bites man, was not found on rats. 



Tidswell, who made his observations during the latest plague epidemic 

 at Sydney, reports that he collected one hundred fleas from rats, of 

 which ten were identified as Pulex fasciatus, eight as Typhlopsylla musculi, 

 one as Pulex serraticeps, and eighty-one as Pulex pallidus. Tiie last one, 

 it appears, has not previously been mentioned as occurring on ordinary 



