XV 

 DESCRIPTION OF PLATES 



THE drawings were made by Miss Etta R. Piotti to whom we express our 

 thanks and appreciation. 



All of the illustrations except Fig. 10 of Plate II were made from prepara- 

 tions, sections, or smears, stained with Giemsa's stain. 



The drawings are accurately made to scale with the camera lucida. Un- 

 less otherwise stated, the photomicrographs are exactly the number of 

 diameters specified. 



PLATE I 



FIGURE 1. Louse Box 60, Louse 9. Rickettsia prowazeki. 



2,000 diameters. Smear. This preparation is made by the dissection of 

 the gut of an experimentally infected louse. In the field are many 

 rickettsias. They appear as granules and short rods disposed singly or 

 in pairs. The irregularity of size and staining of the organisms forming 

 the pairs is clearly shown. There are also in the field short chains 

 composed of two or more paired organisms. 



FIGURE 2. Louse 4 from Dr. Weigl. Rickettsia rocha-lima. 



2,000 diameters. Smear. This preparation was made from a louse of the 

 Commission's American stock which had been maintained on himself 

 by Dr. Weigl. Such lice invariably became infected with the organism 

 illustrated. To it Dr. Weigl has given the name Rickettsia rocha- 

 lima. The organisms exist as granules or short rods which lie singly 

 or in pairs. Their irregularity in size and staining reaction is clearly 

 seen. Among the rickettsias lie many organisms which are considerably 

 above the average in size; such organisms, as well as the small ones, 

 often unite to form short rods. Dr. Weigl recognizes pleomorphism as 

 one of this organism's characteristics. 



FIGURE 3. Mr. Bacot's stock. Louse 2. Rickettsia pediculi. 



2,000 diameters. Smear. This preparation was made on the tenth day 

 of Mr. Bacot's attack of trench fever (see page 130) with one of the 

 stock lice maintained by him. The smear, made by the dissection and 

 teasing out of the gut of the louse's viscera, shows many rickettsia 

 bodies. The organisms occur as granules and short rods which are 

 disposed singly or in pairs. One of the numbers of a pair is often smaller 

 than the other and difference in staining between the chromatinic 

 granules and ground substance composing the organisms is seen. 



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