INFECTIOUS DISEASES OF MICE 427 



splenectomy, has been produced (63, 77), whereas hi splenectomized rats 

 immediate infection appeared (52, 32, ^^, 63, 122). McCluskie and Niven 

 (167), however, failed to confirm these results. Infection of splenectomized 

 rabbits has been successful in some hands (35, 37), but not in others (120). 

 Certain individual splenectomized voles {Microtus pennsylvanicus) have 

 been found to be susceptible (296). 



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Fig. 165. — Epcrytlirozooii coccoidcs. Spontaneous infection in splenectomized 

 laboratory mouse. Note organisms on the margins of the erythrocytes and free in 

 the plasma. Giemsa. (X900.) {Courtesy of Dr. D. Weinman.) 



The role of the spleen in this infection appears to be entirely similar to 

 that in bartonellosis. No satisfactory attempts to demonstrate immunity 

 have as yet been made. 



Etiology. — Eperythrozoon coccoides characteristically appears in the 

 blood of infected animals as a small gram-negative ring- or disk-shaped 

 organism (Fig. 165), occurring either attached to the surface of erythrocytes 

 or free in the plasma (237, 51, 52, 167, 63, 163, 331). It may be visualized 

 by dark field technique or in dry blood smears stained with Wright's or 

 Giemsa's stains. The rings are fairly uniform, approximately i ju in diam- 

 eter, and have an unstained central zone with a bluish-red or violet periphery. 

 Masses of cytoplasm at one or two points in the circumference may stain 

 more intensely, giving the appearance of polar bodies. Some variation in 

 shape occurs and racquet- or club-like forms may be seen. In addition, fine 

 bacillary and tiny coccoid forms occur, quite distinct from the rod-like 

 appearance of the rings which are viewed on edge. Organisms attache? to 



