SERUM DIAGNOSIS 371 



excision of the gall-bladder, have been tried, success has hitherto 

 not been attained. From the public health standpoint, the 

 prevention of carriers from occurring in a population has been 

 considered, and it is a question whether in fever hospitals 

 means ought not to be taken for retaining convalescents from 

 typhoid until the bodily discharges are free from the typhoid 

 bacillus. This 1ms already been undertaken in the British army 

 in India. 



The Serum Diagnosis of Typhoid Fever. This method of 

 diagnosis is based on the fact that living and actively motile 

 typhoid bacilli, if placed in the diluted serum of a patient suffer- 

 ing from typhoid fever, within a very short time lose their 

 motility and become aggregated into clumps. 



The methods by which the test can be applied have already 

 been described (p. 118). 



(1) It will be there seen that the loss of motility and clumping 

 may be observed microscopically. If a preparation be made by 

 the method detailed (typhoid serum in a dilution of, say, 1 : 30 

 having been employed), and examined at once under the micro- 

 scope, 'the bacilli will usually be found actively motile, darting 

 about in all directions. In a short time, however, these move- 

 ments gradually become slower, the bacilli begin to adhere to one 

 another, and ultimately become completely immobile and form 

 clumps by their aggregation. When this occurs the reaction 

 is said to be complete. If the clumps be watched still longer a 

 swelling up of the bacilli will be observed, with a granulation 

 of the protoplasm, so that their forms can with difficulty be 

 recognised. In a preparation similarly made with non-typhoid 

 serum the individual bacilli can be observed separate and 

 actively motile for many hours. 



(2) A corresponding reaction visible to the naked eye is 

 obtained by the " sedimentation test," the method of applying 

 which has also been described (p. 120). The test in this form 

 has the disadvantage of taking longer time than the microscopic 

 method, but it is useful as a control ; in nature it is similar. 



Such is what occurs in the case of a typical reaction. The 

 value of the method as a means of diagnosis largely depends 

 on attention to several details. The race of typhoid bacillus 

 employed is important. All races do not give uniformly the 

 same results, though it is not known on what this difference of 

 susceptibility depends. A race must therefore be selected 

 which gives the best result in the greatest number of undoubted 

 cases of typhoid fever, and which gives as little reaction a# 

 with normal sera or sera derived from other diseases. 



