292 INFECTION AND IMMUNITY 



been studied with especial care, notably by Nuttall. 41 All who have 

 investigated the subject find the only important source of confusion 

 in the blood of the anthropoid apes. The specificity of the reaction, 

 too, has been found to depend very closely upon the amount of 

 precipitin in the serum employed. If a highly immune serum is 

 insufficiently diluted, the reaction loses much of its specific value. 42 

 This source of error is easily eliminated in practice by careful con- 

 trol and tit-ration of the sera used for the tests. 



Unlike agglutinins, precipitins have, so far, not been demon- 

 strated in normal sera. 43 



Theoretical Considerations Concerning Agglutinins and Precipi- 

 tins. We have seen that Ehrlich evolved his theories of antibody 

 formation from his early views upon the absorption of nutritive 



Cell -used for i 



FIG. 36. EHRLICH'S CONCEPTION OF THE STRUCTURE OP AGGLUTININS AND 



PRECIPITINS. 



substances by the body cells, and we have followed, in more or 

 less detail, the steps of his reasoning as he developed his hypothesis 

 in its application to the antitoxic and the lytic substances. There 

 still remained the agglutinins and precipitins, bodies which because 

 of their individual characteristics can be classed neither with the 

 group of antitoxic, nor with that of the lytic substances. These 

 two antibodies, while by no means identical, possess the common 

 characteristics of being more thermostable than the bacteriolytic 

 substances, and of being insusceptible to reactivation by normal 

 serum. It is plain, therefore, that both agglutinating and precipi- 

 tating reactions take place without the co-operation of complement. 

 The substances which give rise to precipitins and agglutinins, more- 



41 Nuttall, Brit. Med. Jour., i, 1901; ii, 1902. 

 4 -Kister und Wolff, Zeit. f. Medizinal-Beamte, 1902, 

 43 Kraus, loe. cit., and Norris, loc. cit. 



