ANTIBODIES TO PNEUMOCOCCUS 413 



suiting solution was said to contain 14,000 Felton protective units 

 per cubic centimeter. 



The question arose whether the protective principle against 

 Pneumococcus in specific immune serum is actually a protein of 

 the globulin type representing merely an increase in the native se- 

 rum globulin, whether it is a new protein substance associated with 

 but chemically distinct from the natural globulin of serum, or 

 whether it is a non-protein substance sharing some of the physical 

 and chemical properties of serum pseudoglobulin. From time to time 

 various answers have been proposed. The work of Avery, of Banz- 

 haf, and of Felton indicated that the protective antibody is inti- 

 mately associated with the pseudoglobulin fraction of immune se- 

 rum, but the results do not necessarily imply that the antibody is 

 the natural serum globulin. For example, the experiments of Fel- 

 ton and Kauffmann showed that the ratio of protein to protective 

 units can be reduced by selective salting out with ammonium sul- 

 fate. A difference between immune and native serum globulin is the 

 more alkaline isoelectric point of water-insoluble globulin contain- 

 ing protective antibody, as shown by Felton and by Reiner and 

 Reiner. 1133 The unusual alkaline isoelectric point of the purified 

 immune proteins was considered by Chow and Goebel 226 to be its 

 most characteristic property, and the authors believed that this 

 property might be attributed to the relatively high ratio of amino 

 to carboxyl groups present in the protein molecule. 



Chow and Goebel by repeatedly precipitating pneumococcal an- 

 tibody with ammonium sulfate were able to rid the specific pseudo- 

 globulin from much inert protein material, and then by means of 

 potassium acid phthalate they succeeded in effecting a further 

 purification of the pseudoglobulin antibody. Although Huntoon 666 

 believed that the specific protective antibody separated by him 

 from pneumococcal antigen-antibody precipitates was non-protein 

 in nature, Chow and Goebel were of the opinion that the circulat- 

 ing antibodies are in reality modified serum globulins. Confirma- 

 tion of the latter hypothesis has come from the work of Heidel- 



