482 PLAGUE 



Rats and mice can also be infected by feeding either with pure 

 cultures or with pieces of organs from cases of the disease, 

 though in this case infection probably takes place through the 

 mucous membrane of the mouth and adjacent parts, and only to 

 a limited extent, if at all, by the alimentary canal. Monkeys 

 also are highly susceptible to infection, and it has been show r n 

 in the case of these animals that when inoculation is made on 

 the skin surface, for example, by means of a spine charged with 

 the bacillus, the glands in relation to the part may show the 

 characteristic lesion and a fatal result may follow without there 



being any noticeable 



- - ,f~*>f jf* .. lesion at the primary 



*! r* V ** **** sea *- This f ac t throws 



important light on in- 

 fection by the skin in 

 the human subject. The 

 disease may also extens- 

 ively affect monkeys by 

 natural means during an 

 epidemic. 



Paths and Mode of 

 Infection. Plague 

 bacilli may enter the sys- 



through small wounds, 

 cracks, abrasions, etc., 



FIG. 146.-Film preparation of spleen of rat and in snch cases there 

 after inoculation with the bacillus of plague, IS usually no reaction 

 showing numerous bacilli, most of which are a t the site of entrance, 

 somewhat plump. m-, . , ,. . 



Stained with carbol-thionin-blue. x 1000. ims last tact 1S m 



accordance with what 



has been stated above with regard to experiments on 

 monkeys. The path of infection is shown by the primary 

 buboes, which are usually in .the glands through which the 

 skin is drained, those in the groin being the commonest site. 

 Absolute proof of the possibility of infection by the skin is 

 supplied by several cases in which the disease has been acquired 

 at post mortem examinations, the lesions of the skin surface 

 being in the majority of these of trifling nature ; in only two 

 was there local reaction at the site of inoculation. In most of 

 these cases the period of incubation has been from two to three 

 days ; under natural conditions of infection the average period 

 is within five days. While infection may occur by accidental 

 inoculation through small wounds of the skin surface, it appears 



