777 /; TYriluID I!. \CILLUS 277 



more is needed; the result is negative. If marked clumping and 

 immobilization of the bacilli immediately begin and become complete 

 within five minutes, this is termed a marked immediate typhoid 

 reaction, and no further test is considered necessary, though it is 

 always advisable to confirm the reaction with higher dilutions up to 

 1:50 or more, so as to measure the exact strength of the reaction. If 

 in the 1 : 20 dilution a complete reaction takes place within thirty 

 minutes, the blood is considered to have come from a case of typhoid 

 infection, while if a less complete reaction occurs it is considered that 

 only a probability of typhoid infection has been established. By many 

 the time allowed for the development of the reaction with the high 

 dilutions is from one to two hours, but to us thirty minutes with the 

 comparatively low dilution of 1 : 20 seems safer and more convenient. 

 Positive results obtained in this way may be considered conclusive, 

 unless there be grounds for suspecting that the reaction may be due 

 to a previous fairly recent attack. In our opinion the failure of the 

 reaction in one examination by no means excludes the presence of 

 typhoid infection. If the case clinically remains doubtful, the examina- 

 tion should be repeated within a few days. 



USE OF DEAD CULTURES. Properly killed typhoid bacilli respond 

 well to the agglutination test. For the physician at his office the 

 dead bacilli offer many advantages. The reaction is slower than 

 with the living cultures and is observed either macroscopically or 

 microscopically. A number of firms now supply outfits for the serum 

 test. These outfits consist of a number of small tubes containing an 

 emulsion of dead typhoid bacilli. Directions accompany the outfit. 



PROPORTION OF CASES OF TYPHOID FEVER IN WHICH A DEFINITE 

 REACTION OCCURS, AND THE TIME OF ITS APPEARANCE. As the result 

 of a large number of cases examined in the Health Department Labo- 

 ratories, it was found that about 20 per cent, gave positive results 

 in the first w r eek, about 60 per cent, in the second week, about 80 per 

 cent, in the third week, about 90 per cent, in the fourth week, and 

 about 75 per cent, in the second month of the disease. In 88 per 

 cent, of the cases in which repeated examinations were made (hospital 

 cases) a definite typhoid reaction was present at some time during the 

 illness. 



PERSISTENCE OF THE REACTION. In persons who have recovered 

 from typhoid fever this peculiar property of the blood serum may 

 persist for a number of months. Thus a definite typhoid reaction has 

 been observed from three months to a year after convalescence, 

 and a slight reaction, though much less than sufficient to establish a 

 diagnosis of typhoid infection, from one to fifteen years after the disease. 



REACTION WITH THE BLOOD SERUM OF HEALTHY PERSONS AND 

 OF THOSE ILL WITH DISEASES OTHER THAN TYPHOID FEVER. In the 

 blood serum of over one hundred healthy persons examined in the 

 Health Department Laboratories an immediate marked reaction has not 

 been observed in a 1 : 10 dilution. In several hundred cases of diseases, 

 eventually not believed by the physicians in charge to be typhoid 



