494 PLAGUE 



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. 

 Eats and mice da,n 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 shown 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 lesion at the primary seat. This fact 

 throws important light on infection by the skin in the human 

 subject. 



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. 

 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 ; in the majority of these the 

 lesions of the skin surface were of trifling nature, and there 

 was no local reaction at the site of inoculation. It may now, 

 however, be regarded as established that the ordinary mode of 

 skin infection is by means of the bites of fleas containing the 

 bacilli. It had previously been shown that when fleas were 

 allowed to. feed on animals suffering from plague, plague bacilli 

 might be found for some time afterwards in the stomach, and 

 some observers, for example Simond, had succeeded in trans- 

 mitting the disease to other animals by means of the infected 

 insects. Most observers, however, had obtained negative 

 results, and it was only by the work of the Advisory Committee 



