g8 STUDY AND IDENTIFICATION OF BACTERIA 



A pocket made by cutting the skin of a guinea-pig with scissors and extended 

 subcutaneously with scissors or forceps, into which a piece of the suspected plague 

 tissue is thrust with forceps, is more practical than injecting an emulsion with hypo- 

 dermic syringe. 



Mice inoculated at the root of the tail quickly succumb. Rats, this being pri- 

 marily a disease of rats, are of course susceptible. Other rodents, as squirrels, are 

 susceptible. It has been suggested that a rodent, the Siberian marmot, or tarabagan 

 (Arctomys bobac) might be the starting-point of plague outbreaks. In natural 

 plague of rats, the lesions which establish a diagnosis even without the aid of a 

 microscope are dark red, subcutaneous injection of .the flaps of the abdominal walls 

 as they are turned back, fluid in the pleural cavities, cedematous haemorrhagic 



FIG. 32. Pest bacillus involution forms produced by growing on 3% salt agar. 



(Kolle and Wassermann.) 



periglandular infiltration and swelling of the neck glands, and in particular a creamy, 

 mottled appearance of the liver. The neck glands are chiefly involved because the 

 flea prefers to inhabit the skin of the neck. Smears from the spleen will show the 

 oval bacilli. 



A chronic rat plague, which may be a factor in keeping up the disease, is char- 

 acterized by enlargement of the spleen and the presence within it of nodules contain- 

 ing plague bacilli. McCoy has noted that the frequency of the cervical bubo in 

 rats, noted by the Indian Commission (72%), was not found in California. The 

 glands show periglandular infiltration and injection as well as enlargement. 



Recent investigations in India have definitely determined the fact 

 that the flea (Xenopsylla cheopis) is the intermediary in the trans- 

 mission of plague from rat to rat and from rat to man. In primary 

 pneumonic plague the infective nature is very great and appears to be 

 by the respiratory atrium (From man to man). This was the terri- 

 fying type of plague in the black death of the fourteenth century. 



