MORPHOLOGY 135 



These measurements correspond closely to those of da 

 Rocha-Lima who gives 0.3/1 by 0.4/* for single elements and 

 0.3/i by 0.9/* for the paired forms. 



In all smears, in addition to the small forms described above 

 we have noted the presence of small numbers of slightly larger 

 more deeply staining and more uniformly shaped coccoid 

 paired bodies, somewhat lanceolate in shape and devoid of 

 bluish staining intermediate substance. These forms can be 

 recognized in sections of lice and are the forms most easily 

 demonstrable in human tissues. 



In the systematic examination of one hundred and eighteen 

 smears containing Rickettsia prowazeki, the rod-like forms 

 mentioned by da Rocha-Lima with deeply stained polar 

 granules (Fig. 12, plate II) were seen frequently in large num- 

 bers and almost invariably in small numbers. They are pro- 

 portionately most numerous in sparsely infected lice and stain 

 best when embedded in fragments of cytoplasm. The polar 

 granules stain deep red, the body of the rod a light clear blue, 

 their dimensions range from 0.25/i to 0.35^ in width, to Iju to 

 2.5ju in length. Other palely staining rods, much swollen in 

 the central portion and capped at each end with a biscuit- 

 shaped red staining body, occur in the presence of the bacillary 

 forms and probably represent degeneration or involution forms. 

 A third form, which has been described previously only by 

 Otto and Dietrich (1917), has been seen often in smears by us, 

 and is associated with early infection of the louse or of individ- 

 ual cells in the louse. This is a filamentous form (Fig. 13, 

 plate III) and its association with early infection of cells is 

 based upon the study of sections of infected lice. 



For a considerable period in our work we avoided decision 

 upon delicate filamentous forms which appeared only in lice 

 fed upon typhus patients and never in the control lice. Con- 

 stant association of these forms with the minute forms in a 

 single chain of organisms, in the same louse cell, in the same 

 louse or in other lice from the same boxes with the failure to 

 find them in smears from any louse which, though fed upon 

 typhus cases, did not produce typhus when injected into a 



