386 BIOLOGY OF THE LABORATORY MOUSE 



capillaries are not infrequently distended with mononuclear cells. Pneu- 

 monia has been produced experimentally by aspiration of 5. enteritidis (335). 



The bone marrow shows considerable damage, apparently due to the 

 depressant action of a toxic substance liberated from the bacilli. Maturation 

 of the granulocytes is disturbed, and in severe cases a practically com- 

 plete granulocytic aplasia may be present. It is possible that these organ- 

 isms elaborate a leukopenia-producing substance such as has been isolated 

 from the typhoid bacillus by Morgan (174). Complex polysaccharide- 

 phospholipids which are highly toxic and produce hyperglycemia have 

 been isolated from Salmonella strains, but their effect on bone marrow and 

 leukocytes has not been reported. (See Topley and Wilson (287), pp. 

 566-568 for discussion.) 



Pathological changes in the remaining organs are inconstant and are 

 mainly the result of congestion or hyperemia. Occasionally, bacillary 

 emboli can be found in the glomerular tufts of the kidney and elsewhere in 

 capillaries. Focal inflammatory areas may be present in the myocardium. 

 Bacilli are almost always seen in considerable numbers in smears of the 

 blood, liver, spleen, and lymph nodes. 



Etiology. — :As already pointed out, the organisms most commonly found 

 in cases of mouse typhoid are Salmonella typhimurium and Salmonella 

 enteritidis. Other strains of the paratyphoid group occasionally cause 

 sporadic deaths in laboratory or wild mice, but epidemics due to them are 

 rare. 



In general, the organisms of this group are similar in morphology and 

 biochemical reactions which accounts for the several names given to various 

 strains and much of the confusion concerning them in the older literature. 

 The early work of Smith (254), Bainbridge (16), TenBroeck (266), and 

 others (134, 243, 282, 284) did much to clarify the situation. More recent 

 studies of antigenic structure have provided a logical basis for the classifica- 

 tion which has been accepted by the Salmonella Subcommittee of the 

 Nomenclature Committee of the International Society for Microbiology 

 (232). 



The Salmonella* organisms are gram-negative rods, usually motile, 

 which grow aerobically on ordinary media, and form acid and gas from the 

 carbohydrates which they ferment. They do not attack lactose, sucrose, 



* The classification and nomenclature here used are taken from Bergey's "Manual 

 of Determinative Bacteriology" (22), and are based on those of the Salmonella 

 Subcommittee (232). 



