944 DISEASES CAUSED BY FILTRABLE VIRUS 



eases. It appears from this literature that Rickettsia-like micro- 

 organisms may be present in lice fed upon healthy people, as well 

 as in lice fed upon typhus cases, upon trench fever and upon healthy 

 individuals. Recent and important investigations by Wolbach, Todd 

 and collaborators seem to show that all these observations are 

 correct, but that it is likely that the R. prowazeki associated by 

 da Rocha-Lima with typhus differs materially from some of the 

 other Rickettsia bodies. 



All this elaborate work leaves us still considerably in the dark. 

 It is not at all conclusively definite that the Riekettsia bodies are 

 microorganisms, but those who have studied them most carefully 

 seem to feel reasonably sure that they are. Since the organisms 

 cannot be cultivated, positive differentiation between the various 

 observed forms is not possible. The finding, however, of similar 

 appearances in the blood of typhus patients and in tissue sections 

 gives a certain amount of basis for tentative etiological suggestions. 

 In a separate section taken largely from Wolbach 's description, we 

 have given the general characterization of Rickettsia bodies as a 

 class. The R. prowazeki of da Rocha-Lima, like the others, is very 

 small, being rarely more than two micra in length, and often much 

 less, is non-motile, is hard to stain, gives a reddish-blue color with 

 Giemsa and is found intracellularly particularly in the gastric and 

 intestinal epithelium of the mouse. In typhus patients we have 

 already mentioned the similar bodies seen by Ricketts and Wilder 

 in the blood, and Prowazek found similar bodies within the leu- 

 cocytes of typhus blood. This has been confirmed by Lipschiitz 

 and others. 



Attempts to identify the Plotz bacillus and other organisms with 

 the Rickettsia do not seem logical at the present time since the 

 Plotz bacillus can be cultivated with relative ease, while Rickettsia 

 bodies cannot be cultivated. It is very difficult to stain them, and 

 they decolorize by Gram, The painstaking work of Wolbach, Todd 

 and their associates is not yet published. It will be very shortly 

 published, however, in Wolbach 's Harvey Lecture and the reader 

 is referred to this article. 



Prevention of Typhus Fever. From what has been said above, 

 it is plain that the prevention of typhus fever must be centered 

 chiefly upon delousino-, both of patients and of the population as 

 a whole. Delousirig methods will be dealt with in speaking of the 

 general prevention of louse-borne diseases at the end of this section. 



