640 FILTERABLE VIRUSES— RICKETTSIA 
M oHIity .^Motility has not been observed. They exhibit Brownian 
movement under dark-field ilhimination. 
Staining Reactions.— The Rickettsia stain feebly, or not at all even 
with the more powerful anilin dyes. They do not retain the Gram 
stain. Polychrome eosin methylene blue stains, as Giemsa, color 
them rose-red, the ends of the bodies being rather more deeply stained, 
suggesting bipolar granules. Adventitious bacteria that may be 
present are colored deep purple. 
Growth in Artificial Media.— The organisms of this group, with the 
possible exception of Rickettsia melophagi,i have thus far not been 
cultivated outside of the human or insect host. 
Relation of Rickettsia to Bacteria and to Protozoa.— Opinion is divided 
as to whether Rickettsia are true bacteria, or protozoa. Their staining 
reactions are similar to certain Treponemata; their parasitic relations 
to certain insect hosts, and their refractoriness to artificial cultivation 
suggests relationships with the protozoa. Judgment must be with- 
held until much more is known about the group. 
The Known Rickettsia.— The following members of the group of 
of Rickettsia have been recorded : it should be remembered that iden- 
tification of the members of this group at the present time is based 
rather upon their occurrence in specific hosts than upon distinctive, 
individual peculiarities. In other words, classification at present predi- 
cates host specificity. 
Rickettsia. 
1. Rickettsia rickettsii^ . 
(Dermacentoxenus rickettsii') 
2. Rickettsia prowazeki^ 
3. Rickettsia melophagii 
4. Rickettsia pediculi^ 
5. Rickettsia quintana« 
6. Rickettsia wolhynica' 
7. Rickettsia cetenocephali* 
8. Rickettsia lectularis' 
9. Rickettsia trichodectse^" . 
10. Rickettsia linognathi" 
Typhus Fever (Tabardillo, Brill's Disease).— Typhus fever is an 
acute, infectious febrile disease of man, characterized by an incubation 
1 NoUer: Arch. f. Schiffs. u. Tropen Hyg., 1917, 21, 53; Berl. kliii. Wchnschr., 1916, 
53, 778. 
2 Ricketts: Jour. Am. Med. Assn., 1909, 52, 739. 
3 Wolbach: Jour. Med. Res., 1919, 41, 1. 
4 Hegler and v. Prowazek: Berl. klin. Wchnschr., 1913, 50, 2035. da Rocha-Lima: 
Berl. khn. Wchnschr., 1916, 53, 567. 
^ Munk and da Rocha-Lima: Mlinchen. med. Wchnschr., 1917, 64, 1422. 
6 Werner and Haenssler: Mlinchen. med. Wchnschr., 1916, 63, 1020. W'erner, 
Benzler and W^eise: Ibid., 1916, 63, 1369. Werner and Benzler: Ibid., 1917, 64, 695. 
Schmincke: Ibid., 1917, 64, 961. 
7 Toepfer: Mlinchen. med. Wchnschr., 1916, 63, 1495. 
8 Sikora: Arch. f. Schiffs. u. Tropen. Hyg., 1918, 22, 442. 
9 Arkwright, Atkin and Bacot: Parasitology, 1921, 13, 152. 
10 Hindle: Ibid., 1921, 13, 152. 
11 Ibid., p. 152. 
Found in 
Human 
the alimentary canal of 
disease. 
Dermacentor venustus 
Rocky Mountain 
spotted fever. 
Pediculus humanus 
Typhus fever. 
Melophagus ovinus 
Pediculus humanus 
Trench fever? 
Pediculus humanus 
Trench fever? 
Pediculus humanus 
Trench fever? 
Ctenocephalus canis 
? 
Cimex lectularius 
? 
Trichodectes pilosus 
? 
Linognathus stenopsis 
? 
