626 PATHOGENIC MICROORGANISMS 



house rats and is characterized by subcutaneous induration, swelling of 

 lymph nodes, with, later, falling out of the hair, emaciation, and some- 

 times ulceration. Its course is protracted and rats may live with it 

 for six months or a year. When a rat suffering from this disease is dis- 

 sected there is usually found, under the skin of the abdomen or flank, a 

 thickened area which has the appearance of adipose tissue except that 

 it is more nodular and gray and less shiny than fat. It is so like fat, 

 however, that it is often overlooked by those unfamiliar with the 

 condition. In this area acid-fast bacilli looking like the Bacillus leprae 

 are found in large numbers. These bacilli are also found in the lymph 

 nodes and sometimes in small nodules in the liver and lung. 



The disease can be transmitted experimentally from rat to rat and 

 probably is transmitted naturally from rat to rat by the agency of 

 fleas (Wherry, McCoy). Although clinically not exactly like human 

 leprosy the condition is sufficiently like it to arouse much hygienic 

 interest. The distribution of the disease in various parts of the world 

 does not correspond with the distribution of leprosy. A peculiar 

 feature of its distribution is the- fact that in San Francisco, as the writer 

 was told by McCoy, almost all the rats that suffered from this disease 

 came from the district in which the retail meat business is located, 

 known as "Butchertown." The organisms were made to multiply in 

 vitro by Zinsser and Gary in plasma preparations of growing rat spleen. 

 Chapin has succeeded in cultivating them by a method analogous to 

 the trypsin-egg albumen method employed by Duval. In the experi- 

 ments of Zinsser and Gary it was found that although the organisms 

 may retain their acid-fast characteristics for many weeks within leu- 

 cocytes they degenerate rapidly within the spleen cells, a fact which 

 seems to have some bearing on the mechanism of resistance possessed 

 by the body against acid-fast organisms, 



