BACILLUS PESTIS 231 



places in Asia, including the Philippine Islands, to Europe, Africa, 

 Australia, and also invaded the western shores of the United States. 

 The great epidemic in India and China still exists, and is annually 

 killing hundreds of thousands of people. The disease is particularly 

 interesting to the veterinarian, not merely from a general human, but 

 from a special professional standpoint, because it is a natural disease 

 of some rodents, more especially of the various varieties of the common 

 rat. That rats die extensively during plague epidemics had been 

 noticed in the Middle Ages, and certain statements occur in the Bible 

 which evidently refer to rodents dying from plague. The investi- 

 gations in particular of the English Indian Plague Commission and 

 the Advisory Committee for Plague Investigation in India have 

 demonstrated the great prevalence of acute plague among the rats 

 and its relation to the spread of the disease to man. 



Pathologic Lesions of Plague in Rats. It is of the greatest practical 

 importance to recognize plague in rats. It frequently, if not generally, 

 precedes plague in man, and the human disease cannot be stamped 

 out successfully in a territory unless it is eliminated among the rats. 

 Fortunately, plague in rats can be diagnosticated easily and generally 

 by means of the naked eye without an additional microscopic examina- 

 tion. The plague bacillus, both in rats, other animals, and man, tends 

 to invade the lymph glands nearest to its place of entrance, and there 

 multiplies enormously, leading to very characteristic changes, such as 

 swelling, edema, and hemorrhages into the gland and the neighbor- 

 hood of the periglandular region. Later the gland may contain pus 

 or a necrotic caseous material. A gland presenting the indicated 

 pathologic changes is called a bubo, and, hence, the disease, which so 

 regularly leads to the formation of such buboes, is known as bubonic 

 plague. The gland lying closest to the place of infection and first 

 suffering marked pathologic changes is called the primary bubo of the 

 first order. If neighboring glands are affected by direct continuous 

 transport of the bacilli they are known as primary buboes of the second 

 order. The distant glands which become infected through the blood 

 circulation or through the lymph circulation are known as secondary, 

 tertiary buboes, etc. The Advisory Committee for Plague Investiga- 

 tion reported on the examination of over 31,000 rats in Bombay, 

 India, 4000 as infected with plague. The postmortem findings fur- 

 nished the following general picture. Subcutaneous congestion, visible 

 after removing the skin of the animal, is not infrequently a well- 

 marked feature. It may be general, but in some cases is limited to 

 the bubo. A peculiar purplish-red appearance of the muscles exposed 

 by reflecting the skin of the thorax and abdomen is obviously due to 

 the presence of congested vessels, and combined with the reddish- 

 pink color of the subcutaneous tissue is a strong indication of plague 

 at the beginning of the examination. Subcutaneous hemorrhages are 

 frequently noticed particularly in the submaxillary region; here also 

 edema is common; general edema over the entire body is quite rare. 



