592 Plague 



of his experiments upon this point was great enough to prove that 

 plague cannot be thus spread. Vergbitski,* however, was more 

 successful and a bed-bug that he caused to bite a patient suffering 

 from plague, subsequently transmitted the disease to a rat. It is 

 quite possible that mosquitoes and biting flies may transmit it. 



M. Herzogt has shown that pedicuh may harbor plague baciUi 

 and act as carriers of the disease. 



As epidemics of human plague are commonly preceded by epi- 

 demics among the ra,ts which die in great numbers, it early became 

 a question whether the plague among them was not caused by the 

 bites of fleas, and whether it might not also be fleas that infected 

 man. 



Ogata f found plague bacilli in fleas taken from diseased rats. 

 He crushed some fleas between sterile object-glasses and introduced 

 the juice into the subcutaneous tissues of a mouse, which died 

 in three days with typical plague, a control-animal remaining well. 

 Some guinea-pigs taken for experimental purposes into a plague 

 district died spontaneously of the disease, presumably because of 

 flea infection. 



Galli-Valerio§ and others thought that the fleas of the mouse and 

 rat were incapable of living upon man and did not bite him, and 

 that it was only the Fttlex irritans, or human fl^a, that could transmit 

 the disease from man to man. Tidswell||, however, found that 

 of loo fleas collected from rats- — there were four species, of which 

 three — the most common kinds — bit men as well as rats. Lisbon** 

 found that of 246 fleas caught on men in the absence of plague, only 

 one was a rat flea, but out of 30 fleas caught upon men in a lodging- 

 house, during plague, 14 were rat fleas. This seems to show that 

 as the rats die off their fleas seek new hosts, and may thus contribute 

 to the spread of the disease. 



That fleas can cause the transmission of plague from animal 

 to animal has been proved by experiments made in India. These 

 experiments, which are published as " Reports on Plague Investiga- 

 tions in India," issued by the Advisory Committee appointed by 

 the Secretary of State for India, the Royal Society, and the Lister 

 Institute, appear in the "Journal of Hygiene" from 1906 onward.ff 

 It seems from these experiments that human fleas (Pulex irritans) 

 do not bite rats, but that the rat fleas of all 'kinds do, though not 

 willingly, bite men. By placing guinea-pigs in cages upon the floor 



* "Jour, of Hygiene," 1904, viii, 185. 

 t "Amer. Jour. Med. Sci.," March, 1895. 

 t " Centralbl. of Bakt. in Parasitenk., 1897, xxi, p. 769. 

 § Ibid., XXVII, No. I, p. I, Jan. 6, 1900. 

 II "Brit. Med. Jour.," June 27, 1903. 

 ** "Times of India," Nov. 26, 1904. 



tt "Journal of Hygiene," Sept., 1906, vol. vi, p. 421; July, 1907, vol. vii, p. 

 324; Dec, 1907, vol. VII, p. 693; May, igo8, vol. viii, p. 162; 1909, vol. ix; 1910, 

 vol. x; 1911, vol. XI. 



