100 The Nature of Precipitin Reactions 



this respect to the sero-precipita studied by other authors, and it also 

 differed in being soluble in concentrated urea solutions, and in saturated 

 solution of magnesium chloride. The egg-white precipitum, on the 

 other hand, he found to be soluble in dilute acids and alkalis 1 , whereas 

 he was unable to confirm the observation of Myers (1900) to the effect 

 that this precipitum is soluble in 2 "/ saline. It proved insoluble in 

 solutions of alkaline carbonates, and various solutions, even up to 

 saturation point, of sodium chloride. Acid solutions of precipitum were 

 reprecipitated 1 on being neutralized, behaving like an acid albumin. 

 When washed in saline and heated, the precipitum coagulates, and 

 is then insoluble in weak acids, behaving therefore like coagulated 

 albumins which have undergone clotting through corresponding fer- 

 ments and have then been coagulated by heat. 



The precipitum, obtained by adding anti-ox serum (from rabbit) to 

 ox serum as described under " Observation III." (p. 89), examined by 

 Mr Hopkins last year, was found to be soluble in very dilute NaHO, 

 much less easily soluble in Na^CO,,. It was precipitated from alkaline 

 solution on neutralization, but was soluble in excess of acid, even acetic. 

 The precipitum contained abundant phosphorus in organic combination. 

 It gave the biuret, xanthoproteic, and glyoxylic reactions, and was found 

 to contain " loosely bound " sulphur. 



Macroscopic and Microscopic Appearances during Reaction. 



When antiserum is added to blood dilution, it sinks to the bottom 

 of the tube. If it does not mix with the dilution, but flows down the 

 walls of the vessel, the reaction taking place almost instantaneously at 

 the zone of contact, assuming that the antiserum is powerful, and 

 reacting with its homologous blood dilution. The reaction consists in 

 the formation of a milky layer at the point where antiserum and blood 

 dilution come in contact. The milkiness extends gradually upward, 

 until the whole fluid is clouded. Where the fluids have been partially 

 mixed this generalized clouding occurs more rapidly, being perfectly 

 uniform when the bloods are thoroughly mixed by shaking. Where the 

 fluids have been mixed by shaking the diffuse clouding undergoes 

 a change ; after 10 to 20 minutes, or later, very fine granules of pre- 

 cipitum begin to appear, and the upper layers of fluid begin to clear, due 

 to the sedimentation of the particles of precipitum. The fine particles 

 soon become aggregated into coarser ones, and these into flocculi, which 



1 Also observed by Michaelis (9, x. 1902, p. 734). 



