EXPERIMENTAL INOCULATION. 441 



observers with extensive experience have doubted its occurrence. 

 In the various forms of the disease the bacilli occur also in the 

 blood, in which they may be found during life by microscopic 

 examination, chiefly, however, just before death in very severe 

 and rapidly fatal cases. In most cases, however, they cannot be 

 detected in the blood by this means, though in some of these 

 they may be obtained by means of cultures. 



The above types of the disease are usually classified together 

 under the heading pestis major, but there also occur mild forms 

 to which the term pestis minor is applied. In these latter there 

 may be a moderate degree of swelling of a group of glands, 

 attended with some pyrexia and general malaise, or there may 

 be little more than slight discomfort. Between such and the 

 graver types, cases of all degrees of severity are met with. 



Experimental Inoculation. Mice, guinea-pigs, rats, and 

 rabbits are susceptible to inoculation, the two former being 

 on the whole most suitable for experimental purposes. After 

 subcutaneous injection there 

 occurs a local inflammatory 

 oedema, which is followed 

 by inflammatory swelling of 

 the corresponding lymphatic 

 glands, and thereafter by a 

 general infection. The le- 

 sions in the lymphatic glands 

 correspond in their main char- 

 acters with those in the human 

 subject, although usually at the 

 time of death they have not 

 reached a stage so advanced. 



By this method Of inoculation Fl f a ^Fihn preparation of spleen of 



; ^ rat alter inoculation with bacillus of plague, 



mice Usually die in 13 days, showing numerous bacilli, most of which are 



guinea-pigs and rats in 2-5 

 days, and rabbits in 4-7 days. 

 Post mortem the chief changes, in addition to the glandular 

 enlargement, being 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. 152), and also, though in somewhat less degree, through- 

 out the blood. Infection can also be produced by smearing the 



