ISOLATION OF THE BACILLUS 473 



7. Precipitins. 



[The addition of plague serum to a filtrate of the plague bacillus produces 

 first a cloudiness then an abundant precipitate which settles to the bottom of 

 the tube leaving the supernatant liquid clear.] 



[A filtrate of the B. pseudo-tuberculosis rodentium added to plague serum gives a 

 similar but less abundant precipitate and the fluid takes much longer to clear. ] 



SECTION IV. THE ISOLATION AND IDENTIFICATION OF THE 

 BACILLUS. POST MORTEM APPEARANCES IN NATURALLY 

 INFECTED RATS. 



In the living subject the pus of the buboes, 1 the juice of the lymphatic 

 glands, the blood (obtained by pricking the finger or lobe of the ear), sputum, 

 [urine,] and the fluid in the petechise must be examined for the presence 

 of the bacillus. 



Even when there is an absence of buboes, the bacillus is present in the 

 lymphatic glands : in such cases, remove a gland and examine it as detailed 

 below. 



In the dead body the spleen, lungs, kidneys, etc. should be examined. 



The technique of identification of the bacillus is as follows : 



1. Microscopical examination. Prepare films on slides, fix in alcohol-ether, 

 stain with carbol-thionin or carbol-violet. Stain other films by Gram's 

 method the plague bacillus is gram-negative. 



[Microscopical examination alone cannot be relied upon for the recognition 

 of the plague bacillus : the B. pseudo-tuberculosis rodentium, organisms of 

 the pasteurella and often of the salmonella group are indistinguishable from 

 the plague bacillus under the microscope.] 



2. Cultures. Sow the gland pulp or scrapings from the viscera on agar 

 and incubate at 37 C. 



[To examine the blood collect 2 c.c. of blood by means of a sterile syringe from a 

 suitable vein at the bend of the elbow (p. 193) and distribute in small quantities on 

 a series of agar slopes. ] 



Haffkine has described an ingenious and rapid method for the identification of 

 cultures of the plague bacillus. The method consists in sowing the suspected 

 material in broth on the surface of which a layer of sterilized butter or oil has been 

 poured (p. 468). Under these conditions the plague bacillus gives origin to stalac- 

 titic forms of growth suspended from the lower surface of the oil. [This appearance 

 is seen with only a few other organisms, namely : the bacilli of the hsemorrhagic sep- 

 ticaemia group, but these happen to be just the organisms which are likely to be 

 confounded with the plague bacillus. The formation of stalactites in broth culture 

 cannot therefore alone be accepted as a sufficient diagnostic feature.] 



3. Inoculation experiments. Inoculate a loopful of growth from an agar 

 culture beneath the skin of a mouse or guinea-pig or into the nasal fossse of a 

 guinea-pig. If the culture be a growth of the plague bacillus the animal will 

 die in 2-5 days and the organism can be recovered from the blood, spleen, etc. 



When dealing with material containing many adventitious organisms, such 

 as stools, decomposing carcases etc., it is best to rub a little of the suspected 

 material into a previously shaved area of skin of a guinea-pig (p. 463). 



[In examining urine for the presence of the plague bacillus, the Advisory 

 Committee adopted both the cutaneous and the sub-cutaneous inoculation 

 methods, and obtained better results than previous observers who had relied 

 mainly on cultivation methods.] 



1 In bubonic pus the plague bacillus is occasionally associated with staphylococci, 

 the colon bacillus, etc. In suppurating buboes the specific bacillus may have disappeared. 



