CALVIN B. COULTER 311 



found that alterations in the hydrogen ion concentration produced no 

 change in the electrical properties of the bacteria; their original nega- 

 tive charge was not neutralized at the optimal point for agglutination 

 and was not reversed by a more acid reaction. Arkwright* found, 

 however, two optimal zones for acid agglutination of typhoid bacilli; 

 in the more acid zone (pH 3.0) agglutination of the bacterial bodies 

 is associated with absence of electrical charge. In the less acid zone 

 (pH 4.7 to 3.5) a soluble bacterial protein precipitates and no change 

 in charge is noted. 



As to the influence of specific sensitization very little is known. 

 Neisser and Friedemann^ observed that agglutinin bacteria flocculate 

 in the electric field as a direct result apparently of the electric flow. 

 Michaelis and Davidsohn^" conclude that specific typhoid agglutina- 

 tion and precipitation are independent of the H concentration, al- 

 though from their tables for agglutination it appears that there is an 

 optimum for this phenomenon lying between pH 4.6 and 3.7 very close 

 to that of the native bacteria, which is at pH 4.4. 



EXPERIMENTAL. 



The isoelectric point was determined in the present work by the 

 method of cataphoresis, using a model of U-tube evolved after experi- 

 ments with many types of apparatus. It is illustrated in Fig. 1. 

 The non-polarizable electrodes consist of zinc rods inserted through 

 perforated rubber stoppers into the long ends of large stop-cock tubes. 

 The lower portion of these tubes and the cock itself are filled with 

 15 per cent zinc sulfate solution. The upper part of these tubes con- 

 tains a buffer solution of acetic acid acetate or phosphate mixture. 

 This solution is made up to 10 per cent of saccharose, in order to have 

 a specific gravity less than that of the zinc sulfate and greater than 

 that of isotonic (m/4) saccharose solution alone, to minimize diffusion 

 when the different fluids are in contact. The U-tube itself has an 

 inside diameter of 6 mm. and a total length of 30 cm. It is made in 

 two equal portions, so that after filling the side arms including the 



' Arkwright, J. A., Z. Immunitdtsforsch., Orig., 1914, xxii, 396. 

 ^ Neisser, M., and Friedemann, U., Milnch. Med. Woch., 1904, li, 465, 827, 

 ^"Michaelis, L., and Davidsohn, H., Biochem. Z., 1912, xlvii, 59. 



