672 A MANUAL OF BACTERIOLOGY 



relationship of the Eickettsia bodies remains, therefore, 

 very problematical. " Tabardillo " seems to be a local 

 form of typhus fever occurring in Mexico. 



The Weil-Felix reaction is a remarkable agglutination 

 reaction which occurs with the blood of typhus fever. 

 Weil and Felix isolated from the urine of a case a race of 

 Proteus, known as X 19 . The race is peculiar in that it 

 exhibits specific agglutination with typhus blood -serum. 

 The same organism has since been isolated by other 

 observers, both from the urine and from the blood, but 

 only occasionally (e.g. 20 times in 350 blood samples 

 from 250 typhus cases. Schiirer and Wolff). It is gener- 

 ally considered to have no setiological relationship with 

 the disease. 



The blood serum of normals and non-typhus cases 

 usually has little agglutinating power on Proteus X 19 ; 

 some 10 per cent, of normal human sera will agglutinate 

 up to a dilution of 1 in 50. On the other hand, typhus 

 blood-serum agglutinates Proteus X 19 in dilutions of 

 from 1 in 100 to 1 in 10,000. The reaction is so constant 

 with typhus blood, and so constantly absent with the 

 blood in other diseases, that it forms a valuable means 

 for the diagnosis of typhus fever. The reaction appears 

 about the seventh day of the disease and increases in 

 intensity up to the twentieth or thirtieth day, after 

 which it declines. Agglutination obtained with serum 

 in dilution of 1 in 100 or more indicates typhus fever. 

 Absence of agglutination in dilution of 1 in 100 after the 

 eighth day from onset of the disease excludes acute 

 typhus fever. 1 



Typhus blood-serum does not agglutinate ordinary 

 strains of Proteus. Agglutinins, moreover, are generally 

 thermostable, but the typhus agglutinin for Proteus X 19 



1 See Reynolds, Journ. Roy. Army Med. Corps, July, 1920, p. 1. Also 

 Fairley, Journ. of Hygiene, vol. xviii, 1919, p. 203. 



