60 CLINICAL BACTERIOLOGY AND 



thought at first the serum taken from a patient suffering 

 from a specific disease had the specific agglutinating power 

 only, but later it was demonstrated that the undiluted serum 

 of normal persons was capable of producing the same effect. 

 It was then decided to dilute the serum. Thus, one loopful 

 of serum was mixed with nine loopfuls of a young fresh 

 bacterial emulsion. Then the strength was made 1 in 50, 

 and when the patient was suffering from the specific dis- 

 ease the agglutinating power would still be in evidence. 

 The length of time allowed for agglutination to take place 

 is usually half an hour. 



Widal's Test for Diagnostic Purposes. 



Collect the blood from the patient in a Wright's capsule. 

 Allow the clot to shrink, to squeeze out the serum ; or, to 

 hasten the process, centrifugalize it, placing the capsule in 

 the centrifuge, having, of course, previously sealed the 

 straight end of the capsule. In this way we obtain our 

 serum. We now take a young culture, preferably grown 

 on broth, make a hanging drop, microscopically examine 

 the specimen, and note the disposition and motility of the 

 bacteria. 



We then take a capillary pipette, make a unit mark with 

 the grease pencil on the stem high enough up to contain 

 1 to 2 cm., aspirate one unit of serum, a bubble of air, one 

 unit volume of 0*86 per cent, saline solution, a bubble of 

 air, one volume of saline solution, and so on, until we have 

 taken up fourteen volumes of the solution, each separated by 

 a column of air. The whole is now expelled from the pipette, 

 and again aspirated to thoroughly mix, and further dilu- 

 tion of this dilution is made — usually three dilutions, 

 1 in 15, 1 in 25, 1 in 50. 



Three hanging-drop slides are next prepared. One loopful 

 of the diluted serum should be placed on three cover-glasses 

 (1 in 15, 1 in 25, 1 in 50), and to each is added and mixed 

 one loopful of broth culture containing the organism. The 

 hanging drops are now examined under the micro- 



