Appearances during Reaction 101 



gradually sinking to the bottom of the tube give rise to more or less 

 deposit, having, when pure serum is used, a whitish appearance. Particles 

 may adhere to the walls of the tube, from which they are readily de- 

 tached by rotating it. With blood dilutions of, say 1 : 40 to 1 : 200 and 

 over, the deposit formed is usually sharply defined, where more con- 

 centrated dilutions are used the deposit may form an irregular mass at 

 the bottom of the tube. The increased viscidity of such dilutions may 

 retard sedimentation. The supernatant fluid remains clear. In some 

 few cases it may remain slightly clouded, more especially in non-homo- 

 logous blood dilutions. In rare instances where non-homologous, but 

 related bloods are tested, a cloud may form, without, however, leading 

 to a deposit. 



Similar appearances are noted when anti-human serum is added to 

 albuminous urine, as described by Leclainche and Vallde (25, i. '01), 

 who made their tests by bringing equal volumes of antiserum and urine 

 in contact with each other in the manner described above. In testing 

 with lactosera the opacity of milk diluted to 1 : 40, as recommended by 

 Wassermann and Schtitze, prevents one following the finer details of 

 the reaction. In this case the antiserum may be added in the pro- 

 portion of 1 : 1 or 1:5 as recommended by the last-named author. 

 Here the casein is precipitated by the antiserum. 



The reaction may be followed microscopically, as recommended by 

 Tarchetti (1901), and Modica, who used the "hanging-drop" method, 

 familiar in bacteriological work. Griinbaum (18, i. 1902) used this 

 method also, comparing the appearances to what is seen when bacteria 

 are agglutinated, and observed that the particles appeared and were 

 more rapidly aggregated when anti-human serum was added to human 

 than to simian blood-dilution and vice versa. Robin (20, xii. '02) also, 

 apparently unaware of Tarchetti's method, has found it useful, for he 

 reports that he could observe the formation of granules within 10 to 15 

 minutes microscopically, when a reaction visible to the naked eye was 

 only observable after two hours. He considers that the aggregation of 

 granules is possibly brought about by a process analogous to that of 

 bacterial agglutination. 



The Supernatant Fluid. 



If antiserum is added in insiifiicient amount to a blood dilution the 

 supernatant fluid, after removal of the first deposit, still contains pre- 

 cipitable substance, as may easily be proved by adding more antiserum, 

 and vice versa. 



