TYPHOID FEVER. 387 



upon the stage of a microscope and examined for the 

 agglutinations. 



As recent extended observations have shown that occa- 

 sionally the blood of healthy men and animals has the 

 power of producing the agglutinations, the consensus of 

 opinion now seems to be in favor of the view that a cer- 

 tain dilution of the blood is required for a satisfactory 

 diagnosis, and that all reactions with concentrations 

 greater than one part of blood in fifty of culture may be 

 questionable, while less concentrated dilutions are almost 

 positively diagnostic. A time-limit must be placed upon 

 the experiment. For the weak dilution not more than 

 two hours should be required for a perfect reaction, and 

 for the stronger solution correspondingly less time should 

 be required. 



A curious fact that should not be overlooked is that the 

 agglutinating substance is not constantly present in the 

 blood, but sometimes alternates, being present for several 

 days and then absent for a day or two. 



The agglutinating power of the blood occurs early in 

 the course of typhoid, and in typical cases seems to be 

 present in the first week of actual illness. 



A point that should not be forgotten is that the agglu- 

 tination of the bacilli seems to be a phenomenon quite in- 

 dependent of any immunity possessed by the individual, 

 and therefore is not an "immunity-reaction." Just what 

 the agglutinating substance is, has not yet been determined. 



The agglutinations are occasionally caused by the 

 serum and dried blood from other diseases than typhoid, 

 but in a collection of 4000 cases it was shown that the 

 errors from this source were only about 5 per cent. 



Malvoz l has experimented with a number of chemicals, 

 and has found that formaldehyd, corrosive sublimate, per- 

 oxid of hydrogen, strong alcohol, and anilin colors (such 

 as chrysoidin, vesuvin, and safranin) have the power to 

 produce the typical agglutinations even in very dilute 

 solutions. 



1 Ann. de T Inst. Pasteur, xl., 7, 1897. 



