352 BAQTEBIOLOGY. 



finally encountered that gives the reaction most conspic- 

 uously and quickly with genuine typhoid serum. This 

 culture is then to be set aside to be used for this test 

 with serums from doubtful cases of the disease. In the 

 hands of all those who have employed this method care- 

 fully for the diagnosis of typhoid fever the results are 

 reported to have been almost uniformly satisfactory. 

 The reaction is, so far as experience indicates, specific — 

 i.e., a typical reaction does not occur between typhoid 

 serum and organisms other than the typhoid bacillus, 

 nor between the typhoid bacillus and serums other than 

 those of typhoid fever. There are, however, confusing 

 reactions — so-called pseudo-reactions — in which more or 

 less clumping of the bacilli and a diminution of motion, 

 without complete cessation, are observed. These have 

 been seen to occur with normal blood and with blood 

 from other febrile conditions. It is said by Johnston 

 and McTaggart^ that they can be prevented if cultures 

 of just the proper degree of vitality are employed. The 

 method is yet in the experimental stage,- and there are 

 still numerous features that are not entirely clear. It 

 is, however, in the light of present experience, fair 

 presumptive evidence that the serum is from a case of 

 typhoid fever when unmistakable agglutination and 

 cessation of motion are seen in typhoid bacilli that are 

 mixed with the serum of a suspicious febrile condition. 

 For the hanging-drop test sufficient serum may be ob- 

 tained from a needle-prick in the finger, while for the 

 tes1>tube reaction a larger amount is needed; this may 

 be obtained from blood drawn from a superficial vein 

 by means of a hypodermic syringe, or from the 

 cleansed skin by a wet-cuj:), or, better still, from a 

 small cantharides blister. 



I Johnston and McTaggart : Montreal Medical Journal, March, 1897. 



