Mode of Infection 



S9I 



died in from three to seven days. In these cases the local edema 

 observed by Yersin did not occur. They point out the interest 

 attaching to infection through so insignificant a wound and without 

 local lesions. Weichselbaum, Albrecht and Gohn have found that 

 rats may be infected by rubbing the infective material upon the 

 surface of the shaved skin, the method being employed for making 

 a diagnosis of the disease in suspected cases. Rats and mice in- 

 fected through the skin usually die in two or three days, guinea- 

 pigs in two to five days, rabbits in three to eight days. 

 The facihty with which dermal infection could be brought about, 



Antepygidial bristle 

 Pygidium 



Stigmata 

 Penis „J 



Abdomen 



Thorax Head 



;'' _. Ocular bristle 

 Oral bristle 



Maxillary palp 

 Maxilla 



Fig. 234. — Xenopsylla cheopis (male) (from Rothschild). 



quickly suggested that the skin might be the common route, and 

 that biting insects might act as vectors. 



Yersin showed that flies taking up the bacilli may die of the in- 

 fection. Macerating 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 observa- 

 tion correct, and showed that flies fed with the cadavers of plague- 

 infected mice die in a variable length of time. Large numbers of 

 plague baciUi were found in their intestines. 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 



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



