392 BIOLOGY OF THE LABORATORY MOUSE 



spreads readily to normal animals by contact, presumably by means of 

 respiratory and conjunctival secretions, and is dependent on carriers for its 

 continuation. The mortality varies between 75 and 100 per cent. Post- 

 mortem findings consist of subserosal and submucous hemorrhages, fibrino- 

 purulent exudations in the pleural, pericardial, and peritoneal cavities, and 

 hemorrhagic consolidation of variable extent in the lungs. The spleen is 

 seldom enlarged and other visceral organs show httle or no gross change 

 beyond the exudate over their surfaces. In the more chronic disease, 

 enlargement of the lymph nodes and small necrotic foci in the liver may be 

 present. Pasteurella organisms are found in large numbers in the blood, 

 spleen, and inflammatory exudates in acute cases, but may be obtained only 

 with difficulty from animals surviving for several days or longer. 



Experimentally, mice are readily infected by Pasteurella of this group 

 regardless of the animal source of the organism. Numerous routes of 

 administration are effective — conjunctival, dermal, subcutaneous, intra- 

 peritoneal, intravenous, oral, and respiratory (139, 300, 173). Parenteral 

 administration produces an acute, fulminating septicemia terminating by 

 death in i or 2 days. Postmortem findings consist of local edema and con- 

 gestion, fibrinous exudate over the serous surfaces, enlargement of the spleen, 

 and pulmonary edema and congestion. Administration by other routes 

 results in a more chronic infection, lasting up to a week or longer and char- 

 acterized by more pronounced local reactions depending somewhat on the 

 route of administration. Pathological changes are similar to those found 

 in the spontaneous disease. 



The causative agent is Pasteurella muricida (B. fnurisepticus) (22, 173). 

 Morphologically, the organism is a short, oval, bipolar gram-negative rod, 

 which is non-motile and measures about 0.3 ix in width and 1.25 /i in length. 

 Growth occurs aerobically on ordinary media at a wide range of tempera- 

 tures (20° to 37°C.). No growth occurs on bile media. Dextrose, levulose, 

 galactose, sucrose, and mannose are fermented with the production of acid; 

 indol is formed and nitrates reduced. Serologically, this organism cannot 

 be distinguished satisfactorily from other members of the hemorrhagic 

 septicemia group isolated from different animal species and named accord- 

 ingly. Topley and Wilson (287), however, have found two distinct types 

 of P. muricida, distinguishable by agglutination and maltose fermentation. 



Diagnosis of the disease in the acute form can usually be made only by 

 identifying the organism, since the clinical and pathological findings are not 

 specific. In chronic cases, recovery of the organism by culture often fails 

 and inoculation of a normal mouse or guinea pig with tissue emulsions 



