182 PATHOLOGY 



filth seem to be conditions favorable to infection with 

 this germ. Just how the infection occurs is not known, 

 but it is suspected that bed-bugs or fleas may be instru- 

 mental in its transference. 



Morbid Anatomy. There are no characteristic ana- 

 tomic alterations in this disease. Ecchymoses of the 

 skin occur, and there have been found enlargement of 

 the spleen, cloudy swelling of the heart, liver, and 

 kidneys, and infarcts of the kidney and spleen, also 

 changes in the bone-marrow. 



Morbid Physiology. No toxins have been demon- 

 strated in this disease, but antibodies for the germs are 

 developed during each paroxysm of fever that rapidly 

 destroy the germs, which are then taken up by the 

 phagocytes. Some, however, appear to withstand the 

 effects of the antibodies and develop and multiply after 

 an interval, either because of the partial disappearance 

 of the antibodies or to an immunity of the surviving 

 germs. When growth and development of the germs 

 begin again, another paroxysm of fever occurs, which is 

 ended as before by the development of antibodies and 

 phagocytosis. The blood becomes finally so charged 

 with antibodies that further growth of the germs is im- 

 possible, and recovery occurs, with immunity to further 

 infection. The blood of such immune animals confers 

 immunity on animals injected with it, and is also cura- 

 tive when infection has already occurred. 



