INFECTIOUS DISEASES OF MICE 435 



manifestations form a prominent part of the clinical picture and are almost 

 pathognomonic. Enlargement is noted in one foot — usually a hind foot — 

 which presents a swollen translucent appearance due to edema of the sub- 

 cutaneous tissues. As the edema increases, exudation of serous fluid occurs 

 through the skin and crusting takes place over superticial ulcers. \'esicles 

 may also form. The diseased skin is usually sharply demarcated from 

 healthy tissue by a line of constriction, and gangrene of a toe or the foot may 

 follow, with ultimate separation of the foot at this line. Recovery ordinarily 

 occurs in these cases, and the animals are then immune to subsequent expo- 



FiG. 167. — Infectious ectromelia: left, advanced lesions of foot and leg; right, normal 

 mouse. {From McGaughey and Whitehead, J . Path, and Bacf.) 



sure or inoculation. Should the disease spread to involve any or all of the 

 other feet, the tail, or the skin around the mouth or over the body, death 

 invariably results (Fig. 167). 



Pathology of the natural disease. — Mice dying acutely show an increase 

 in peritoneal, pleural, and pericardial fluid which at times may be abundant. 

 Serous membranes, especially those of the intestines, are markedly con- 

 gested. The liver is usually pale and anemic or greyish-brown in appearance 

 and soft and necrotic in consistency. The spleen is ordinarily normal in size 

 or but slightly enlarged, and may be either studded with yellowish-grey areas 

 of necrosis or present an appearance of massive necrosis. Congestion is 

 present in the lymphatic glands, lungs, and sometimes the adrenal cortex. 

 Xo organisms can be found by direct smear or by culture of the exudate or 

 organs. Aside from generalized congestion and occasional small hemor- 



