TYPHUS FEVER 109 



Of twenty-four cases tested before the crisis all were negative except two 

 which were tested one day before the crisis, both of which had a titre of 1 : 100. 

 Of ten cases tested on the day of the crisis, three were positive and seven nega- 

 tive. After the crisis, thirty-eight cases were studied, 92.6 per cent, of which 

 were positive. Agglutinins have been demonstrated as late as five months 

 after the crisis. Of a very large series of control cases, no case gave a reac- 

 tion in a dilution above 1 : 50, except three cases in which the occurrence of 

 a previous attack of typhus fever could not be excluded. In these cases the 

 reactions varied from 1 :100 to 1 : 200. Control studies made by testing the 

 serum of typhus cases against various other organisms were negative. 



The opsonic index increases at the crisis and remains high in the 

 convalescent stage. 



The organism is a small gram-positive bacillus, from 0.9 to 1.93 microns 

 in length, the breadth being from one-fifth to three-fifths of the length. It is 

 not acid-fast, has no capsule, and polar bodies can be demonstrated by appro- 

 priate methods. When first isolated, it grows only anaerobically, but after a 

 time it can be grown aerobically. 



Intraperitoneal inoculation of a pure culture of the organism into guinea- 

 pigs produces a rise of temperature in from twenty-four to forty-eight hours, 

 the temperature remaining high for four or five days, and then dropping by 

 crisis. This corresponds to the reaction seen in guinea-pigs after inoculation 

 with defibrinated blood from typhus fever patients, except that the incubation 

 period is shorter. Serum from a convalescing typhus patient has bactericidal 

 properties against the organism obtained from Brill's disease and typhus fever. 



