136 RICKETTSIA PROWAZEKI IN LICE 



guinea-pig, compelled us to accept them as a form of Rickettsia 

 prowateeki. 



These filamentous or thread-like forms in smear prepara- 

 tions are usually curved, sometimes sharply flexed in one or 

 several places (Fig. 8, plate II). In width they range from 

 0.3ju to 0.4ju and in length are often extraordinary, 10/z to 40ju 

 or 5(V (Fig. 9, plate II). The threads stain blue and the out- 

 lines seem unbroken though varying slightly in width in the 

 same filament. Within the blue stained filaments are red 

 stained bodies in pairs and chains corresponding in dimensions 

 to the free lying rickettsia bodies. Some of the thread forms 

 stain homogeneously pale blue. Within a single filament 

 (Fig. 8, plate II) the arrangement of the red stained bodies 

 suggests the division of the whole into any one of the previously 

 described forms, coccoid bodies, the thick or slender bi-polar 

 bacillary, and all forms, singly, in pairs, and in long or short 

 chains. In occasional preparations we can identify portions 

 of crushed epithelial cells from the louse gut filled with enor- 

 mous numbers of filamentous, rod, and coccoid forms with ap- 

 parent stages in the formation of the two latter forms from 

 the former (Figs. 13 and 29, plates III and IX). 



The early occurrence of these filamentous forms is borne out 

 by finding them in sections of lice lying curled within non- 

 swollen cells of the mid gut at a time when very few cells are 

 infected with the coccoid rickettsia. Similar bacillary and 

 thread-like or filamentous forms have been described by Ark- 

 wright, Atkins, and Bacot as a part of the developmental 

 cycle of a rickettsia-like (Rickettsia lectularius) parasite of the 

 bedbug (1921). These authors suggest that the small Rickett- 

 sia lectularius bodies develop through the bacillary stage into 

 filaments while others continue to multiply by simple fission. 

 The filamentous forms finally break up into the minute rick- 

 ettsia bodies. An intracellular development of minute forms 

 also leads to the formation of larger lanceolate paired forms 

 from which bacillary and filamentous forms develop. 



