134 RICKETTSIA PROWAZEKI IN LICE 



The double contour seen with most bacteria under dark field 

 illumination does not show with Rickettsia prowazeki. Da 

 Rocha-Lima states that rickettsia do not differ from bacteria 

 in their power to refract light. 



1. SMEAR PREPARATIONS OF LICE 



The rickettsia of typhus literature is a small bacterium-like 

 micro-organism, ovoid or elliptical in shape, usually occurring 

 in pairs. (Figs. 12, 14, and 18, plates II, III, and IV.) Short 

 and long rods with polar bodies and coccoid and bacillary 

 bodies in short chains have been described (Fig. 13, plate III). 

 The ovoid coccoid form in pairs is usually regarded as the 

 type form. The two elements composing the pairs stain 

 deeply with Giemsa's stain, taking a red coloration while the 

 material between the two stains pale bluish. Where the organ- 

 ism occurs singly there is often a zone of pale blue material 

 surrounding or tapering from the deeply staining red ovoid 

 body. The minute paired forms, while composed usually of 

 ovoid elements, are often composed of two pyriform elements 

 joined at their narrow extremities lying in a straight line or 

 forming an obtuse angle. These pyriform elements may be 

 unequal in size. They stain blue and contain in their distal 

 extremities red stained, round, ovoid, or ellipsoidal bodies. 

 They seem to be a variation or possibly a divisional stage of 

 the blue staining rod form with polar bodies described below. 

 (Fig. 15, plate III.) 



The minute coccoid and paired coccoid forms were invariably 

 present in greater or less numbers in all our preparations from 

 rickettsia infected lice. 



Measurements by us from negatives of photomicrographs, 

 made accurately at 2,000 diameters and read under low mag- 

 nification with a micrometer ocular calibrated so as to make 

 ten divisions of the scale equal one millimeter, give the follow- 

 ing dimensions. The smallest single elements range from 

 0.25/z by 0.4ju to 0.3/* by 0.45ju. The paired forms range from 

 0.25ju by O.Tju to 0.3ju by I. In. (The above method of measuring 

 micro-organisms is probably accurate to 0.05^0 



