RATS AND PLAGUE H^ 



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 



FIG. 33. Pest bacillus involution forms produced by growing on 3% salt agar. 

 (Kolle and Wassermann.) 



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

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

 mottled appearance of the liver. 



The bacillus known as Danysz virus also causes whitish granules of 

 liver but these are larger and do not have the appearance as if peppered 

 on the liver. 



The neck glands in rat plague are chiefly involved because the flea prefers to 

 inhabit the skin of the neck. The spleen is swollen, congested and granular and 

 smears from this viscus will show the 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 transmis- 

 sion of plague from rat to rat and from rat to man. 



