MORPHOLOGY 137 



2. RICKETTSIA PROWAZEKI IN SECTIONS OF LICE 



Sixty-two of the lice sectioned from the experimental boxes 

 contained Rickettsia prowazeki. Seven of these also contained 

 extracellular rickettsia which, because of their position upon 

 the cuticular borders of the cells, deep staining and uniform 

 morphology, we decided to call Rickettsia pediculi. The stain- 

 ing technic employed by us stains Rickettsia prowazeki in sec- 

 tions blue or purplish blue. Rickettsia pediculi stain purple 

 red or red. 



In a few lice the only evidence of rickettsia was the presence 

 of one or a few non-swollen cells filled with bacillary to thread- 

 like forms. A larger number contained only a few cells filled 

 with bacillary forms (Fig. 28, plate IX) and these cells were 

 sometimes not swollen or more often swollen and even ap- 

 peared as pedunculated projections into the lumen of the gut 

 (Fig. 30, plate IX). 



In all lice where a large number of cells were infected, the 

 minute coccoid form predominated, and cells containing these 

 are usually swollen to many times their normal size and are 

 easily recognizable with low power objectives (Figs. 24 and 

 25, plate VII). The multiplication of these coccoid forms 

 leads finally to rupture of the cells. Two types of small dip- 

 lococcoid bodies can be recognized within cells in sections, 

 and these correspond to forms seen in smears; one staining 

 blue or bluish, the smallest recognizable form of rickettsia, 

 and the other slightly larger, lanceolate and more deeply 

 stained (Figs. 26 and 31, plates VIII and IX). If the differen- 

 tiation of the stains is carried far enough or if the slides after 

 completion are bleached in sunlight these more deeply stained 

 pairs retain a purple red color and seem always to be within 

 vacuoles. 



In the lightest, and therefore probably the earliest, infec- 

 tions observed in lice, the organisms have been bacilliform. 

 The rickettsia have always been bacilliform in lice where pro- 

 longed search has resulted in the discovery of a single infected 

 cell. From our observations it is not possible to state whether 



