126 RICKETTSIA 



The following data concerning the rickettsia in the preced- 

 ing table are available. 



Rickettsia melophagi: This micro-organism was discovered 

 by Noller in 1917 while studying flagellates of the sheep louse 

 or tick. He succeeded in cultivating it upon a glucose blood 

 agar medium. Jungmann in 1918 confirmed Noller's work, in- 

 cluding the cultivation, and determined that the infection of 

 the insect host is hereditary. Rickettsia melophagi is not 

 pathogenic, it occurs characteristically upon the cuticular 

 surface of the epithelium of the sheep louse's stomach; but 

 it may invade the cells. In morphology it corresponds to the 

 small or coccoid forms of Rickettsia pediculi and Rickettsia 

 prowazeki; it is not pleomorphic. 



The unnamed rickettsia from the dust louse, Psocus, de- 

 scribed by Sikora in 1918-20, is not associated with any 

 mammalian host. It is transmitted hereditarily, lives wholly 

 extracellular in the stomach of its host, and is non-pathogenic. 

 Sikora was unable to infect Pediculus with this rickettsia. 



Rickettsia pediculi, Rickettsia quintana, and Rickettsia wolhy- 

 nica (Plate I, figs. 3 and 4) are morphologically indistinguish- 

 able and in all probability are identical (Wolbach and Todd, 

 1920), (Bacot, 1921). They are on the whole easier to stain 

 than Rickettsia prowazeki, and are much more uniform in 

 morphology. They are slightly plumper and more definitely 

 oval than Rickettsia prowazeki. They occur characteristically 

 extracellular in the louse's stomach and adhere to the cuticular 

 border of the stomach epithelium in a striking manner (Plate 

 V, fig. 20). Sikora and others maintain that exceptionally 

 Rickettsia pediculi invades the epithelial cells of the louse's 

 stomach. We have not been able to find evidence of intracellu- 

 lar distribution or multiplication of the rickettsia acquired by 

 the stock lice fed upon Mr. Bacot during his illness with 

 trench fever although twenty-six were examined by serial 

 section. It is transmitted hereditarily in the louse. The virus 

 of trench fever (and therefore Rickettsia pediculi, if we are 

 correct in our conclusions) resists a dry heat of 80 C. for 

 twenty minutes, and ordinary dessication in sunlight for 



