Diagnosis 577 



Ogata found plague bacilli in fleas taken from diseased 

 rats. He crushed some fleas between sterile object-glasses 

 and introduced the juice into the subcutaneous tissues of 

 a mouse, which died in three days with typical plague, a 

 control animal remaining well. Some guinea-pigs taken for 

 experimental purposes into a plague district died sponta- 

 neously of the disease, presumably because of insect infection. 



The animal most prone to spontaneous infection seems to 

 be the rat, and there is much evidence in support of the view 

 that it aids in the spread of epidemics. In several of the 

 Asiatic plague districts and at Santos the appearance of 

 plague among the inhabitants was preceded by a large mor- 

 tality among the rats, which examination showed had died 

 of plague. 



Galli-Valerio * and others think that the fleas of the mouse 

 and rat are incapable of living upon man and do not bite 

 him, and that it is only the Pulex irritans, or human flea, 

 that could be capable of transmitting the disease from man 

 to man. Tidswell,f however, found that of 100 fleas col- 

 lected from rats, there were four species, of which three 

 the most common kinds bit men as well as rats. Lisbon J 

 found that of 246 fleas caught on men in the absence of 

 plague, only one was a rat flea, but out of 30 fleas caught 

 upon men in a lodging-house during plague 14 were rat fleas. 

 This seems to show that as the rats die off, their fleas seek new 

 hosts and may thus contribute to the spread of the disease. 



It may be that the fleas, while not themselves making 

 the inoculation, deposit the bacilli in their feces upon the 

 skin, into which it is carried by the finger-nails when the 

 bites are scratched. M. Herzog has shown that pediculi 

 may harbor plague bacilli and act as carriers of the disease. 



Diagnosis. It seems possible to make a diagnosis of the 

 disease in doubtful cases by examining the blood, but it is 

 admitted that a good deal of bacteriologic practice is neces- 

 sary for the purpose. 



Abel found that blood-examinations may yield doubt- 

 ful results because of the variable appearance of the con- 

 tained bacilli, which may easily be mistaken for other bac- 

 teria. He deems the best tests to be the inoculation of 



* " Centralbl. f. Bakt. u. Parasitenk.," Jan. 6, 1900, xxvn, No. 1, p. 1. 

 t " British Med. Journal," June 27, 1903. 

 J" Times of India," Nov. 26, 1904. 

 "Amer. Jour. Med. Sci.," Mar., 1905. 

 37 



