ORGANIC DISEASES OF THE RAT, INCLUDING TUMORS. 



By GEORGE W. McCoy, 

 Passed Assistant Surgeon, United States Public Health and Marine-Hospital Service. 



The lesions described here are those that have been found in the 

 routine examination of rats for plague infection in the federal labora- 

 tory at San Francisco during the past year, in which time approxi- 

 mately 120,000 rats have been examined. 



As the subject had no special bearing upon the plague investi- 

 gations, but little time was spent in examining and recording the 

 nature of organic lesions that were observed. Notes, however, were 

 made of many of the conditions which were encountered, and these 

 notes have been used as the basis of this paper. 



It is well known that various lower animals are subject to some of 

 the so-called organic diseases from which man suffers, and not a 

 little experimental work has been done in endeavoring to establish in 

 animals certain of the lesions commonly found in human pathology. 



Usefulness of wild rats for laboratory purposes. 



We would call special attention to the fact that wild rats suffer 

 spontaneously from cirrhosis of the liver, fatty degeneration of the 

 liver, nephritis, and calculi of the urinary tract, and would, therefore, 

 probably furnish excellent subjects for the experimental investigation 

 of these diseases. 



The objection may be made that the very fact that these animals 

 do suffer from these diseases spontaneously makes them unsuitable 

 for experimental purposes, as one could not be certain that any 

 lesions found were not spontaneously developed rather than that they 

 were due to the conditions imposed in an experiment. In reply to 

 this objection we would say that the most of these organic lesions 

 occur so rarely in rats in nature that one could almost ignore them. 



The ease with which wild rats are obtained and the readiness with 

 which they adapt themselves to the conditions of life in captivity 

 are factors which should make them more extensively used for labo- 

 ratory purposes than is the case at present. We have described 

 (New York Medical Journal, Feb. 6, 1909) the methods that have 

 been found useful in keeping and handling these rodents. Without 



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