ANTIGENS, HAPTENS, ANTIBODIES, ETC. 427 



antiserum by allowing it to react with the corresj^onding 

 antigen and dissociating the antigen-antibody complex 

 by an- appropriate means. H^emolysins have been elnted 

 from sensitised red blood corpuscles with dilute acid or 

 with glycine ; the eluates contained about 40 to 80 X 10~^ 

 mg. of solid per hsemolytic unit. Agglutinins have been 

 recovered from sensitised typhoid bacilli by extraction 

 with dilute alkali, but with considerable loss ; no protein 

 could be detected, but the nitrogen content was 0-4 mg. 

 per 100 ml. Ramon dissociated the diphtheria toxin- 

 antitoxin complex and obtained solutions containing 

 0-012 mg. of protein per unit of toxin. Northrop has 

 obtained crystalline diphtheria antitoxin by digesting 

 the toxin in the floccules with tiypsin and crystallisation 

 from ammonium sulphate solution. The purified anti- 

 toxin has molecular weight about 80,000, has an electro- 

 phoretic mobility of 4x 10~^ cm. per second per volt per 

 cm., at pH 7-3. It contains about one million antitoxin 

 units per gram of protein nitrogen. Pneumococci have 

 been agglutinated by the corresponding antiserum and 

 the complex dissociated by extraction wdth dilute alkali ; 

 the eluates were colloidal, did not give the ordinary 

 protein reactions, and were not attacked by trypsin ; the 

 antibody was not precipitated by 30 j)er cent, sodium 

 chloride nor by dilution as w^ould be globulins, but as the 

 solutions contained only 0-00015 mg. of nitrogen per unit 

 this lack of reactions is not surprising. 



The most satisfactory results on these lines are those 

 in ^vhich pneumococcus antisera have been precipitated 

 by the protein-free soluble specific polysaccharides and 

 the antibodies then separated from the precipitates. 

 Felton decomposed the precipitates from Types I and II 

 antisera with calcium or strontium hydroxide solutions 

 in which the protein is soluble but which give insoluble 

 precipitates wdth the polysaccharides. The antibody was 

 then precipitated from solution by dialysis, behaving like 

 euglobulin ; the activity was destroyed by proteolytic 



