PATHOLOGY 147 



The presence of a fibrinous exudate upon the spleen and 

 omentum has often been found in guinea-pigs which exhibited 

 no evidences of secondary infection during life, i.e., no short- 

 ening of the incubation period or unusual height of tempera- 

 ture. The inoculation of blood from such an animal into the 

 peritoneal cavity of other guinea-pigs was usually, but not 

 invariably, followed by a similar exudate while a subcutaneous 

 inoculation was usually but not invariably followed by a nor- 

 mal peritoneum at autopsy. This appearance we feel certain 

 is due to a secondary infection. In many guinea-pigs with 

 moderately enlarged spleen we have found the spleen to be 

 covered with a very thin transparent layer of fibrin-like ma- 

 terial with normal peritoneum elsewhere. Smears as well as 

 sections from such spleens show that this layer is composed 

 of mononuclear cells and fibroblasts, without polymorpho- 

 nuclear leucocytes and without demonstrable micro-organisms, 

 and we believe that this delicate coating limited to the spleen 

 is compatible with an uncomplicated typhus infection. 



Nicolle and his associates unfortunately have given no de- 

 tailed description of the pathology of typhus in guinea-pigs. 

 They merely state that pathological changes are absent. 



Otto and Dietrich (1918) note the following gross changes: 

 swelling of the axillary and inguinal lymph nodes, slight swell- 

 ing and reddening of the adrenal glands and minute hemor- 

 rhagic infarcts of the lungs and liver. They also state that 

 the muscles may appear dry and friable and that the spleen is 

 usually not notably enlarged. 



Plotz, Olitsky, and Baehr (1915) note enlargement of the 

 spleen. 



Loewy (1916) has described microscopically visible lesions 

 on the under surface of the skin in typhus guinea-pigs. This 

 we have not seen ourselves, and Otto and Dietrich (1918) also 

 failed to find such skin lesions. 



