642 FILTERABLE VIRUSES— RICKETTSIA 
Others,^ however have failed to obtain the Plotz baciUus from un- 
doubted cases of typhus fever. The filterable virus theory also has 
not been confirmed.-' 
Weil and Felix^ isolated two strains of B. proteus (X2 and X19) from 
the urine of typhus cases which would clump with typhus sera. These 
organisms are typical members of the proteus group: they ferment 
glucose and saccharose with the production of gas and acid, but fail 
to ferment lactose, mannose and mannitol. They are somewhat less 
vigorous in their proteolytic activities, however, than many strains of 
the group.'* These bacilli, however, have no etiological relationship 
to typhus fever. 
Notwithstanding the fact that proteus X2 and proteus X19 have no 
apparent etiological relationship to typhus fever, a very useful diag- 
nostic method has been developed for this disease, using these cultures 
as test organisms for homologous agglutinins which develop in typhus 
cases.^' *• ^ 
Great interest and significance attaches to the observations of 
Ricketts and Wilder,*^ daRocha-Lima^ and others,^ upon the occurrence 
6i minute rod-shaped bodies (Rickettsia prowazeki) found in lice 
infected from cases of typhus, and found also in the human lesions as 
well. Evidence is accumulating which points to their protozoan nature. 
Otto,^ Wolbach, Todd and Palfrey ^^ and others have shown that lice, 
infested with the Rickettsia bodies, and ground up with salt solution 
when they are thoroughly developed will induce typhus in guinea-pigs 
upon injection. 
Morphology.— Very small ovoid or rod-shaped bodies occurring 
typically in pairs. Larger bacillary and filamentous forms also occur. 
The organisms are quite pleomorphic. They are found in human cases 
of typhus, where they occur characteristically in association with the 
bloodvessels, as globular masses; and in lice, Pediculus humanus, where 
they are found more commonly in close association with the intestinal 
tract. When the Rickettsia are numerous they may be seen with the 
dark-field illumination. 
Size.— The Rickettsia bodies occurring singly measure from 0.8 to 
0.45 microns in diameter and from 0.3 to 0.5 microns in length. The 
paired forms vary in diameter from 0.3 to 0.6 microns, and in length 
from 0.3 to 1 micron. 
Stain.— The organisms are not colored by ordinary bacterial stains; 
even the more powerful dyes, as carbol-fuchsin, fail to impart color, 
' McCoy and Ncill: Public Health Reports, li»17, 32, 841. 
2 Pub. Health Repts., 1909, 24, ISdl, 1941; 1910, 25, 177; 1912, 27. No. 22. 
3 Wien. klin. Wehnsc-hr., 1910, 29, :VA: 1917, 30, 'Am. 
* Bengston: .Jour. Infer. Dis., 1919, 24, 428. 
'' Holt-Harris and Grubbs: Public Health Reports, 1922, 37, 1075. 
6 Jour. Am. Med. Assn., 1910, 54, 463, 1304, 1373. 
' Deutsch. med. Wchnschr., 1916, 42, 1353. 
8 Wolbach, Todd and Palfrey: The Etiology and Pathology of Typhus, 1922. 
9 Med. Klin., 1916, 12, 1143. " Loc. cit. 
