422 '^he Philippine Journal of Science 1913 



exhibited only two of the signs of plague infection; namely, 

 bubo and oedema of the surrounding tissue, and eventual haemor- 

 rhages. 



Besides plague infection, a great number of rats showed 

 purulent conditions from causes other than plague. Abscesses 

 of the lungs were frequently met with, and cervical or axillary 

 buboes are not uncommon in Manila rats. Various pyogenic 

 bacteria were found in the pus of such abscesses. Of the 

 less common was Bacillus pyocyaneus and the pneumobacillus of 

 Friedlander. Chronic plague was excluded in these cases since 

 the animal inoculation failed to produce plague infection. 



More than half of the rats examined harbored parasites in 

 their organs. Echinococcus teniseformis was found in the liver 

 of practically every gray rat, while a small Ascaris and Tssnia 

 diminuta were not uncommon in the intestines. Two rats were 

 found to have sarcosporidiosis, 2.6 per cent showed rat leprosy, 

 and 7.4 per cent trypanosomiasis. One tumor of the mammary 

 gland and one tumor in the axillary region were encountered, 

 while one tumor of the large curvature of the stomach proved 

 to be a chronic inflammatory tumor due to parasites. One 

 peritoneal tumor in a rat {Mus decumanus) gave the impression 

 of a malignant tumor on account of the miliary dissemination 

 in the peritoneum. It was found to consist of muscle and spin- 

 del-cell sarcomatous tissue. Ectoparasites were very seldom 

 noticed, on account of the method of collecting the rats. When 

 present, they were mites and fleas. 



In the naturally infected plague rats the rigidity of the fresh 

 cadaver was pronounced. The primary bubo was in every case 

 cervical. Cervical glands were enlarged and haemorrhagic with 

 slight oedema of the surrounding tissue. The subcutaneous 

 injection extended over the neck and chest. The inguinal glands 

 were small and pigmented. The lungs were collapsed, and 

 showed haemorrhagic foci. The spleen was slightly enlarged, 

 firm, and dark red. The liver was rather large, firm, pale red, 

 with shade of yellow, which was caused by minute yellowish 

 foci thickly scattered throughout the tissue and visible through 

 the capsule. The kidneys were hypersemic. The intestines 

 were without change. The serous membranes were pale with 

 no haemorrhages. 



Histological examination of the tissue of naturally infected 

 plague rats showed the following changes: 



Liver. — The structure of the organ was well marked; the veins dilated, 

 trabeculae slightly compressed, nuclei well stained, and few of the liver 



