EXPERIMENTAL INOCULATION 481 



so that many 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. The examination of the 

 blood by means of cultivation experiments is, however, a much 

 more reliable procedure. For this purpose about 1 c.c. of blood 

 may be withdrawn from a vein and distributed in flasks of 

 bouillon (p. 72). It may be said from the results of different 

 investigators that the bacillus may be obtained by culture in 

 fully 50 per cent, of the cases, though the number will necessarily 

 vary in different epidemics. The Advisory Committee, ap- 

 pointed by the Secretary of State for India in 1905, found that 

 in some septicuemic cases the bacilli may be present in the blood 

 in large numbers, two, or even three, days before death, though 

 this is exceptional. 



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 

 !>< 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 sub- 

 cutaneous 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 

 lesions in the lymphatic glands correspond in their main 

 characters 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 mice usually die in 1 to 3 days, 

 guinea-pigs and rats in 2 to 5 days, and rabbits in 4 to 7 days. 

 IVst mortem the chief changes, in addition to the glandular 

 enlargement, are congestion of internal organs, sometimes with 

 hemorrhages, and enlargement of the spleen ; the bacilli are 

 numerous in the lymphatic glands and usually in the spleen 

 (Fig. 146), 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. 



