552 



Plague 



when subcutaneously inoculated. When an inoculation was made 

 with a pin dipped in a culture of the bacillus, the puncture being 

 made in the palm of the hand or sole of the foot, the monkeys always 

 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- 



Antepygidial bristle 

 Pygidium 



Stigmata . 

 Penis ... 



Abdomen 



Thorax Head 



Antenna 

 Eye 



Ocular bristle 



Oral bristle 

 - Maxillary palp 

 Maxilla 



" Hip or coxa 



Trochanter 



Femur 



Fig. 230. Xenopsylla cheopis (male) (from Rothschild). v 



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 facility with which dermal infection could be brought about, 

 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 bacilli were found in their intestines. He also found that 

 bed-bugs allowed to prey upon infected animals took up large 

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



