388 THE TYPHOID BACILLUS 



rubber cap. Cultures killed in this way may be stored exactly as chemical reagents 

 are stored in the laboratory. Immediately before use the tube is lightly shaken 

 so that the bacilli shall be uniformly distributed through the medium. To a few 

 drops of this dead culture a few drops of serum are added in the same manner as 

 has been described above. 



There are now a number of preparations of dead bacilli on the market 

 such as Ficker's " Typhus diagnosticum," Stassano's emulsion, etc. These 

 preparations allow the practitioner to perform a serum diagnosis rapidly 

 and easily. The " Typhus diagnosticum " of Ticker in particular has given 

 good results in the hands of many bacteriologists though its reliability is 

 questioned by de Rossi. 



De Rossi advises the use of broth cultures which have been heated to 

 58-60 C. for an hour. The resulting emulsion agglutinates more readily 

 than unheated cultures and preserves its property for at least 3 months. 



Tribondeau uses broth cultures killed by the addition of formalin (1-150) 

 and stored in sealed ampoules. Under these conditions the bacilli retain 

 their capacity for agglutination for 4 years and more. 



Measurement of the agglutinating titre. The serums of different patients 

 vary in their agglutinating powers ; sometimes this power is very feeble 

 while in other cases it is so well marked that clumps are formed when the 

 serum is diluted as much as 1-5000 and 1-15,000 (Jurgens). 



In investigating the agglutinating property of a given serum the examina- 

 tion should be begun with a dilution of 1-10. Agglutination in a lower 

 dilution than this is in no way characteristic, and indeed, since normal human 

 serum occasionally agglutinates when diluted 1 in 10 or even 1 in 20 (vide 

 colon bacillus), a reliable diagnosis can according to Remy only be given 

 when agglutination is found with a dilution of 1 in 50. [Moreover with some 

 serums there appears to be an agglutination-inhibiting action when examined 

 in low dilutions. ] The degree to which the agglutinating power is developed 

 should therefore be measured more exactly by investigating dilutions of 

 1 in 20, 1 in 30 [and so on to at least a dilution of 1-100]. 



In practice when but a small quantity of blood is available two tests suffice, 

 one made with a dilution of 1 in 10 the other with a dilution of 1 in 50. [By 

 the method described above (B. 1. a) if a dilution of -1 in 10 can be obtained 

 a dilution of 1 in 100 and 1 in 500 can also be made. In our experience a 

 dilution of 1 in 100 is the smallest dilution upon which a reliable opinion can 

 be based in suspected cases of enteric fever.] 



Widal and Sicard draw the following distinctions. 



Agglutinating power very feeble if exhibited only in dilutions below 1 in 100. 

 Agglutinating power feeble if exhibited only in dilutions between 1 in 100 and 1 



in 200. 

 Agglutinating power average if exhibited in dilutions 1 in 200 and 1 in 500 



marked 1 in 500 and 1 in 2000. 



,. very marked above 1 in 2000. 



Note. In these measurements it is important that the drops of culture and of 

 the serum be equal in size. A sufficient degree of accuracy is attained by the follow- 

 ing method : take a piece of glass tubing about 20 cm. long and plug it at both 

 ends with wool. Draw it out in the flame as though making a Pasteur pipette. 

 Sterilize the tube without cutting it into two and then, when about to use it, file it 

 in the middle of the capillary portion. In this way, two pipettes are obtained, 

 which for all practical purposes will give drops of equal size : one will serve for 

 the culture, the other for the serum. 



From the point of view of prognosis, it appears that the degree to which 

 the agglutinating power is developed [has no consistent relation to, and 

 therefore] furnishes no reliable information as to the severity of the 

 disease. 



