SERUM DIAGNOSIS 385 



degree by the urine. The blood of a foetus may have little 

 agglutinating effect, though that of its mother may have given 

 a well-marked reaction; sometimes, however, the foetal blood 

 gives a well-marked reaction. It may here also be mentioned 

 that a serum will stand exposure for an hour at 58 C. without 

 having its agglutinating power much diminished. Higher 

 temperatures, however, cause the property to be lost. 



The Agglutination of Organisms other than the B. typhosus 

 by Typhoid Serum. It was at first thought that the reaction in 

 typhoid fever would afford a reliable method of distinguishing 

 the typhoid bacillus from the b. coli. Though many races of 

 the latter give no reaction with a typhoid serum, there are others 

 which react positively. Usually, however, a lower dilution and 

 a longer time are required for a result to be obtained, and the 

 reaction is often incomplete. It has also- been found that other 

 organisms belonging to the typhoid group (v. p. 394) react in a 

 similar way. The reaction as a method of distinguishing between 

 these forms is thus not absolutely reliable, but in certain cases 

 it is of great value in giving confirmation to other tests. The 

 important point here is the determination of the highest dilution 

 with which clumping is obtained (for methods, see p. 121). 

 There is a point in this connection regarding which further 

 light is required. Many races of b. coli in use have been 

 isolated from typhoid cases, and we as yet do not know what 

 effect this circumstance may have on its subsequent sensitive- 

 ness to agglutination by typhoid serum. Again, Christophers 

 has pointed out that a large proportion of serums from normal 

 persons or from those suffering from diseases other than typhoid 

 will clump the b. coli in dilutions of from 1 : 20 to 1 : 200, and 

 no doubt many of the reactions shown by typhoid sera towards 

 b. coli are due to the pre-existence in the individuals of an 

 agglutinative property towards the latter bacillus. 



With regard to the value of the serum reaction there is little 

 doubt. In nearly 95 per cent, of cases of typhoid it can be 

 obtained in such a form that no difficulty is experienced if the 

 precautions detailed above are observed. The causes of possible 

 error may be summarised as follows : The serum of the person 

 may naturally have the capacity of clumping typhoid bacilli ; 

 there may have been an attack of typhoid fever previously with 

 persistence of agglutinative capacity ; the case may be one of 

 disease caused by an allied bacillus ; the disease may have a 

 quite different cause, and yet the serum may react with typhoid 

 bacilli ; the disease may be typhoid fever and yet no reaction 

 may occur. The most important of these sources of error is that 



25 



