IX 

 RICKETTSIA PROWAZEKI IN LICE 



THE gross appearances of lice removed from the experimental 

 boxes was carefully observed in order to ascertain whatever 

 characteristic might appear as indicative of a rickettsia 

 infection. It was suggested (Weigl, 1920) that distended 

 pinkish colored lice which appear in boxes after periods of 

 prolonged feeding are most certainly ones infected with rickett- 

 sia. This we could not confirm as regards color. Lice which 

 remained swollen after forty-eight hours fasting we found to 

 be almost invariably heavily infected with Rickettsia prowazeki. 

 In heavily infected lice digestion is suspended or greatly 

 retarded owing to the loss in function of practically all of the 

 cells of the mid gut due to the packing of their cytoplasm with 

 the rickettsia. The swollen appearance after fasting proved to 

 be the only reliable gross evidence of infection; many lice 

 which were moribund, swollen, or discolored at the time of 

 their removal proved not to be infected. 



Epithelial cells swollen with Rickettsia prowazeki (Figs. 24 

 and 25, plate VII) were frequently seen in the louse's stomach 

 during dissections under the binocular dissecting microscope 

 (magnification of 22.5 diameters). They appear as pale 

 whitish spherules against the dark brown background of in- 

 testinal contents, when obliquely illuminated by reflected light. 



Staining: All our descriptions are based upon preparations 

 stained with dilute Giemsa's stain (see section on technic, 

 p. 12). We made no effort to devise other methods of stain- 

 ing. Our attempts to apply the usual stains employed for 

 bacteria gave the results noted by previous investigators - 

 failure. Rickettsia prowazeki does not retain the stain by 

 Gram's method and will not stain with aqueous solutions of 

 the dyes usually employed as counter stains, Bismarck brown 

 and pyronin. They will not stain with aqueous solutions of 



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