644 FILTERABLE VIRUSES— RICKETTSIA 
from infection with either of the three clinical types is not susceptible 
to infection with the virus of the other two. 
Diagnosis.— //?/?^mn. — l. By the Weil-Felix reaction. ^ Cultures of 
B. proteus, X2 or XI 9 grown upon agar slants for eighteen to twenty- 
four hours are suspended in sterile normal salt solution, and mixed 
with the serum of a suspected case of typhus in dilutions of 1 to 20 to 
1 to 1600. A positive agglutination in a dilution of 1 to 40 usually 
may be regarded as positive.'- Fairley^ has obtained positive agglu' 
tination in 63 out of a total of 65 typical cases of typhus with this reac- 
tion. In 120 control cases, no agglutination was obtained. Wolbach, 
Todd and Palfrey,"* similarly, obtained 80 positive agglutination tests 
out of a total of 83 sera from as many clinical cases, in which the dilu- 
tion of the serum was 1 to 100: 56 of these were positive in a dilution of 
1 to 800 and 26 positive in a dilution of 1 to 1600. 
One serum from a non-typhus case agglutinated in a dilution of 1 to 
50. There is a possibility that this person may have had the disease 
previously. The agglutinins appear to be in maximal concentration 
about the end of the second week of the clinical disease, and persist 
well into convalescence. It is worthy of note that the Weil-Felix 
reaction is either negative, or positive in low concentration, in children 
under ten years of age. This may stand in relation to the well- 
established fact that the disease is usually mild among children. The 
blood of such mild cases, however, is infective for monkeys. It is 
probable that an important sanitary precaution would be the careful 
serological examination of young children in endemic areas to anticipate 
a recurrence of the disease in epidemic form, through proper restriction 
of those found to be infected. 
Wagner,^ and Reichenstein*' and Fairley ^ have reported successful com- 
plement-fixation tests, using proteus X2 and proteus X19 as antigens, 
with typhus serums, but this method is apparently much less satis- 
factory as a routine than the agglutination test. Fairley indeed reported 
80 negative complement-fixation tests out of a total of 83 sera that 
showed positive agglutination with proteus X19. 
Diagnosis of Rickettsia Bodies in Lice.— This is a difficult procedure, 
fraught with many difficulties. Details may be found in the excellent 
monograph of Wolbach, Todd and Palfrey referred to above. 
Prevention of typhus fever, in the light of current information, will 
be coextensive with delousing. It is peculiarly necessary to guard 
against the introduction of typhus into non-infected areas by thorough 
delousing at ports of entry and frontiers. 
Trench Fever (Wolhynian Fever, Fievre de Volhynie, Werner-Hiss 
Disease).— Trench fever is a disease of very low mortality but of high 
' Weil and Felix: Wien. klin. Wchnsohr., 1916, 29, 33; 1927, 30, 393. 
2 Holt-Harris and Grubbs: Public Health Reports, 1922, 37, 1675. 
3 .Jour. Hyg., 1919, 18, 203. 
* The Etiology and Pathology of Typhus, 1922, p. 200. 
6 Munchen. med. Wchnschr., 1917, 64, 792. 
6 Deutsch. med. Wchnschr., 1917, 43, 554. ' ' Jour. Hyg., 1919, 18 203. 
