000 DISEASES CAUSED BY FILTRABLE VIRUS 



primarily adapted to insect tissues, with occasional representatives 

 pathogenic for animals." 



For more detailed analysis of the Rickettsia, we refer the reader 

 to the Harvey Lecture and to the articles on typhus investigations 

 in Poland now being prepared for publication by Wolbach, Todd 

 and their associates. 



Abstracting from the further analysis of the Rickettsia sent us 

 with this table by Wolbach, we may mention the following points. 

 The R. melophagia is not pathogenic and is the only one that has 

 been cultivated upon glucose-blood-agar. The R. cprrodentia of the 

 dust louse is, likewise, not associated with any mammalian host. It 

 lives extracellularly in the stomach of the louse and is apparently 

 non-pathogenic. The R. pediculi quintana and wolhynica are prob- 

 ably identical, according to Wolbach and Todd. They are more 

 uniform in morphology than the typhus one and are easier to stain. 

 They occur extracellularly in the louse's stomach, adhere to the 

 cuticular epithelium, and may invade the epithelial cells. They are 

 transmitted to the egg. Their etiological association with trench fever 

 has been suggested. 



The R. prowazeki is pleomorphic and seems to be exclusively 

 intracellular in the louse. It seems to be more susceptible to drying 

 and to heat than the preceding ones. It is the one studied by da 

 Rocha-Lima and others connection with typhus fever. 



The R. lectularius of the bed bug is non-pathogenic, but mor-. 

 phologically resembles R. prowazeki. 



The ones occurring in mosquitoes and in cat and mouse fleas are 

 non-pathogenic. 



The Dermacentroxenus rickettsi is the Rickettsia body which has 

 been associated by a number of writers with Rocky Mountain 

 Spotted Fever. Wolbach includes it in the general classification, 

 though he has found many differences between it and the other 

 Rickettsia. Wolbach states that it is less bacterium-like than any 

 of the other Rickettsia and many forms show red and blue staining 

 materials. Unlike the Prowazeki, it does not show the thread-like 

 forms. In the louse he states that the Prowazeki continues to mul- 

 tiply in the gastric epithelium and eventually causes the death of 

 the louse by interfering with digestion. The Dermacentroxenus, 

 however, after multiplying within the nucleus chiefly, floods all the 

 tissues of the tick and then diminishes in numbers, leaving behind 

 in the salivary gland and some other tissues, forms which Wolbach 

 regards as a resistant stage. 



