592 Plague 



Mode of Infection. Klein found that animals fed upon 

 cultures of the bacillus or upon the flesh of animals dead 

 of the disease became ill and died with typical symptoms. 

 When he inoculated animals with the dust of dwelling-houses 

 in which the disease had occurred, some of them died of 

 tetanus, one from plague. Many rats and mice died spon- 

 taneously in Hongkong, examination showing the character- 

 istic bacilli. Such infected animals carry the cause of the 

 disease from place to place in their migrations. 



Yersin showed that flies may die of the disease. Macer- 

 ating and crushing a fly in bouillon, he not only succeeded 

 in obtaining the bacillus, but infected an animal with it. 



Nuttall,* in repeating Yersin 's fly experiment, found his 

 observation correct, and showed that flies fed with the ca- 

 davers of plague -infected mice die in a variable length of time. 

 Large numbers of plague bacilli were found in their intes- 

 tines. He also found that bed-bugs allowed to prey upon 

 infected animals took up large numbers of the plague bacilli 

 and retained them for a number of days. These bugs did 

 not, however, infect healthy animals when allowed to bite 

 them; but Nuttall was not satisfied that the number of his 

 experiments upon this point was great enough to prove 

 that plague cannot be spread by the bites of suctorial 

 insects. 



Ogata 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 sponta- 

 neously of the disease, presumably because of insect in- 

 fection. 



The animal most prone to spontaneous infection seems to 

 be the rat, and there is much evidence in support of the view 

 that it aids in the spread of epidemics. In several of the 

 Asiatic plague districts and at Santos the appearance of 

 plague among the inhabitants was preceded by a large mor- 

 tality among the rats, which examination showed had died 

 of plague. Dead rats are usually to be found in plague- 

 infected houses in India. 



Galli- Valerio f and others think that the fleas of the mouse 



* "Centralbl. f. Bakt. u. Parasitenk.," xxi, No. 24, Aug. 13, 1897. 

 t Ibid., xxvii, No. i, p. i, Jan. 6, 1900. 



