CHAPTER XV. 



SPECIAL METHODS OF WORK, Continued. 



Serum Agglutination. 



The normal serum of the blood of various animals on 

 contact with certain motile bacteria (Sanarelli, Eberth, 

 Colon, etc.) will cause these *to clump together or gather 

 into masses. At the same time the individual cells lose 

 their motion and become as it were paralyzed. This phe- 

 nomenon is known as the agglutination reaction. If the nor- 

 mal serum is diluted the reaction will be less intense, and 

 frequently will cease to be given when the serum is diluted 

 with 10 parts of water. Occasionally, a normal serum will 

 still agglutinate in a dilution of 1 : 20 or even 1 : 30. 



In certain diseases, as in typhoid fever, the agglutina- 

 ting substance is greatly increased in amount. The reac- 

 tion then will be surely given with the Eberth bacillus 

 when the serum is diluted 1 : 30, and may be given with a 

 dilution of 1 : 50 or even with greater dilutions. It will be 

 seen, therefore, that the reaction must be quantitative in 

 character when applied to the blood of a suspected typhoid 

 fever case. The following method permits an accurate es- 

 timation of the agglutinating power of a serum. 



The blood is obtained by puncture of the finger and is 

 allowed to clot. The clot can then be loosened with a wire 

 and the mixture centrifugated. The clear serum is used for 

 the test. An abundance of blood, and hence of serum, can 

 be obtained from a vein in the manner described on p. 462. 

 The serum and the diluting fluid should, be measured by 

 means of a drawn-out tube pipette (Fig. 61, p. 457). The 



