SUMMARY 123 



been done, and apparently had not been seriously undertaken 

 until the League of Red Cross Societies sent our Typhus Re- 

 search Commission to Poland. 



English workers, Arkwright, Bacot, and Duncan, and Byam 

 and Lloyd in 1919, presented considerable casuistical evidence 

 for rickettsia as the cause of trench fever. 



A brief summary of our knowledge of rickettsia available 

 at the time of writing, June, 1921, seems desirable and for that 

 reason is presented in this report. 



2. SUMMARY OF PRESENT KNOWLEDGE OF RICKETTSIA 



A satisfactory definition of rickettsia is not possible at 

 present. The properties in common of the thirteen or four- 

 teen micro-organisms so far described under this name are as 

 follows. 



Morphology: Bacterium-like on the whole. They are smaller 

 than bacteria and occur characteristically in pairs. Large 

 forms, bacillary and filamentous, have been described in con- 

 nection with two carefully studied rickettsia Rickettsia 

 prowazeki and Rickettsia lectularius and it seems probable 

 that a simple cycle or sequence in morphological development 

 is a characteristic of the pathogenic forms. 



Staining Reactions: Difficulty of staining with the common 

 staining solutions used for bacteria is a striking feature, as is 

 the failure to retain the stain by Gram's method. The only 

 satisfactory staining methods are the modifications of Roman- 

 owsky's method; of these, the most satisfactory is Giemsa's 

 solution. 



Motility: Motile forms have not been seen. 



Cultivation: So far all have resisted cultivation with the 

 exception of the rickettsia from the sheep louse. It grows on a 

 relatively simple glucose blood agar medium. 



Resistance to Physical and Chemical Agents: Not enough 

 work has been done to generalize. The viruses of typhus 

 (da Rocha-Lima, 1919 2 , p. 240) and Rocky Mountain spotted 

 fever (Wolbach, 1919) are extremely susceptible to heat, dry- 



