EXPERIMENTAL INOCULATION 495 



enlargement, are congestion of internal organs, sometimes with 

 haemorrhages, and enlargement of the spleen ; the bacilli are 

 numerous in the lymphatic glands and usually in the spleen 

 (Fig. 150), and also, though in somewhat less degree, throughout 

 the blood. Infection can also be produced by smearing the 

 material on the conjunctiva or mucous membrane of the nose, 

 and this method of inoculation has been successfully applied in 

 cases where the plague bacilli are present along with other 

 virulent organisms, e.g., in sputum along with pneumococci. 

 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 ex- 

 tent, if at all, by the ali- 

 mentary canal. Monkeys 

 also are highly susceptible 

 to infection, and it has 

 been shown in the case of 

 these animals that when 

 inoculation is made on 

 the skin surface, for ex- 

 ample, by means of a F IG- 159. Film preparation of spleen of rat 

 spine charged with the after inoculation with the bacillus of 



bacillus the fflands in P la g ue > showing numerous bacilli, most of 

 oacnius, ine giana which are somewhat p i ump . 



relation to the part may Stained with carbol-thionin-blue. x 1000. 

 show the characteristic 



lesion and a fatal result may follow without there being any 

 noticeable lesion at the primary seat. This fact throws im- 

 portant light on infection by the skin in the human subject. 

 The disease may also extensively affect monkeys by natural 

 means during an epidemic. 



Paths and Mode of Infection. Plague bacilli may enter the 

 system by the skin surface through small wounds, cracks, 

 abrasions, etc., and in such cases there is usually no reaction 

 at the site of entrance. This last fact is in 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. 



