Inactivated Antisera: Precipitoids 91 



precipitated from inactivated lactoserum by means of dilute acetic acid, 

 for they are absent in the neutralized filtrate. Miiller finds that pre- 

 cipitins do not combine with the neutralizing substance in the presence 

 of (acetic) acid, on the other hand, under similar conditions, the pre- 

 cipitins combine with casein, precipitation occurring although reaction 

 is retarded. Inactivated lactoserum dissolved the precipitum after some 

 hours, whereas inactivated normal rabbit serum did not. Lactoserum 

 robbed of its precipitin by the addition of milk, acquires no neutralizing 

 properties even when heated to 75 C. Mtiller therefore concludes that 

 the neutralizing substances are derivatives of precipitins, originating 

 from these when they are heated. 



Whereas normal inactivated rabbit serum possesses no anti-rennet 

 action, inactivated lactoserum does prevent coagulation through rennet 

 ferment just as it prevents precipitation through fresh lactoserum. He 

 concludes therefore that the neutralizing action depends upon the pre- 

 cipitable (casein) and neutralizing substances combining, thus protecting 

 the casein from the action of the coagulating agents. 



Mtiller considers the neutralizing substances "precipitoids," analogous 

 to the " agglutinoids " recently described by Eisenberg and Volk (see 

 p. 49). According to Ehrlich's theory, the precipitoids would be re- 

 ceptors whose "zymophoric" group has been destroyed by heat, but 

 whose " haptophoric " group is retained (see p. 12). 



Two views may be held with regard to the nature of the neutralizing 

 or combining body in inactivated serum, according to Eisenberg (v. 1902, 

 p. 301). Either, (a) the combining body preexists in unheated serum, 

 its action being obscured by that of the precipitin, or (b) it originates 

 from another substance in precipitin through the action of heat. The 

 latter view, as we have seen, is held by Miiller, and apparently also by 

 Eisenberg. Supposition (a) appears unlikely to Eisenberg, for the reason 

 that if it is correct an excess of precipitatable substance should have no 

 effect in preventing the reaction of the bacterioprecipitin with which 

 Eisenberg experimented. He found, on the contrary, that an excess 

 thereof increased such action 1 . Moreover active serum robbed of its 

 precipitin through the addition of precipitable substance no longer 

 antagonizes fresh precipitin. Neither does deprecipitinated antiserum, 

 as Miiller showed, when heated, prevent the action of precipitins. 



1 See " Observation in " p. 89 where I have stated that an excess may prevent pre- 

 cipitation by haematosera. This statement of Eisenberg's may therefore have to be 

 modified. He was working, however, with bacterioprecipitins which possibly behave 

 differently. 



