THE AGGLUTINATION REACTION 



281 



powder by machinery. The powder may be made up into a suitable 

 suspension by rubbing it in a mortar with normal salt solution. 



(6) When it is necessary to work with highly dangerous microorgan- 

 isms, or to operate from day to day with the same bacterial suspension, 

 one may employ suspensions that have been heated for one hour to 60 

 C., or suspensions in salt solution to which 1 per cent, formalin has been 

 added. These will keep well in the refrigerator, but the sediment of 

 dead bacteria must be well shaken before it is used. 



(b) Serum. Serum should preferably be fresh, clear, and free from 

 corpuscles. 



(1) For the microscopic " wet " method, ample serum is furnished from 

 the blood contained in the ordinary Wright capsule (see p. 33). 



(2) For the microscopic "dry method," blood is secured by pricking 

 the finger or lobe of the ear and collecting a few drops of blood upon 

 aluminum foil, on a clean glass slide, or on partially glazed paper. The 

 blood must not be heated to hasten drying, or agglutinins may be destroyed. 

 Smears on aluminum foil and on glass slides are to be preferred to those 

 on paper, as the blood can be moistened and portions removed without 

 the likelihood of transferring extraneous material, such as paper fiber. 

 While there are certain objections to this method to be pointed out later, 

 yet practical experience has demonstrated its value, as the serum does 

 not readily deteriorate or become contaminated with bacteria, and the 

 ease with which blood may be collected and mailed recommends the 

 process for board of health laboratories. 



(3) For the macroscopic test larger amounts of serum are needed. 

 Sufficient blood is easily obtained by pricking the finger deeply and 

 collecting several cubic centimeters in a small test-tube. 



(4) Because normal agglutinins may be active in dilutions as high as 

 1 : 30, for diagnostic tests in typhoid fever the serum should not be di- 

 luted lower than 1 : 40. For routine work dilutions of 1 : 50 and 1 : 100 

 are well adapted for the microscopic test. Dilutions of 1 : 40 and 1 : 80 

 are readily made with the white corpuscle pipet and are equally useful. 



With the macroscopic technic, dilutions of from 1:20 up to any 

 dilution are readily made in appropriate test-tubes. 



Precautions. In bacteriologic technic due care should be observed 

 to avoid contamination and possible infection when working with living 

 cultures. 



(a) Agglutinated bacteria are not necessarily dead, and hanging-drop 

 preparations, test-tubes, etc., should be immersed in 1 per cent, formalin 

 before cleansing. 



