594 



Plague 



chains of the plague bacillus, occurring in from twenty-four to 

 forty-eight hours. 



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 necessary for the purpose. 



KoUe* has suggested a method valuable both for the diagnosis 

 of the disease and for estimating the virulence of the bacillus. It 

 is as follows: "The skin over a portion of the abdominal wall of 

 the guinea-pig is shaved, care being taken to avoid the slightest 



Fig. 235. — Fig. I is a diagrammatic representation of a longitudinal section 

 through the esophagus (ffi), proventriculus {p), and stomach U) of a heavily 

 infected specimen of Ceratophyllus fasciatus. The light shaded portion shows 

 where fresh blood, impregnated with free individuals of B. pestis, is present in 

 the specimen, the darker shading indicates the solid mass of bacteria which has 

 so far become disintegrated at its center as to be ruptured by the force of the 

 blood pumped into the esophagus, thus allowing the passage of blood to the 

 stomach. The action of the valve is, however, inoperative, owing to the solidity 

 of the mass of bacteria in which the spines of the proventriculus are embedded. 

 X about 180 reduced to one-fourth the size. 



Fig. 2 shows a similar representation of a section through the dissected pro- 

 ventriculus and esophagus of a specimen of C. fasciatus. It differs from Fjg. i 

 in that the lumen of the valve is still obstructed by the disintegrating mass of 

 an old plug and that the growth of bacteria surrounding this, which is of more 

 recent growth, though yielding to the pressure of the fresh blood pumped into 

 the esophagus, has not yet been ruptured. X about 180 reduced to one-fourth 

 the size (Bacot, in Journal of Hygiene). 



injury of the skin. The infective material is carefully rubbed into 

 the shaved skin. Important, in order rightly to understand the 

 occurrence of plague infection, is the fact disclosed here in the case 

 of guinea-pigs, that by this method of inoculation the animals 

 present the picture of true bubonic plague — that is to say, the pro- 

 duction of nodules in the various organs, principally in the spleen. 

 In this manner guinea-pigs, which would not be affected by large 

 subcutaneous injections, even amounting to 2 mg. of agar culture 

 (equal to a loop) of low-virulence plague bacillus, may be infected 

 and eventually succumb." 



* "See Havelburg, "Public Health Reports," Aug. 15, rgoz, vol. xvii. No. 33, 

 p. 1863. 



