312 On the Main Source of " Precipitable" Substance, etc. 



repeated interactions with - 01 gramme or single interactions with 

 01 gramme of antiserum, however minute the original amount of proteicl 

 may have heen. 



That the interaction is of a chemical nature we have no reason to doubt. 

 That a given amount of antiserum will remove from solution definite 

 amounts of its homologous proteid we may accept on the understanding that 

 the amounts of proteid so removed are exceedingly minute. But that is not 

 what is usually meant when it is said that the homologous proteid combines 

 quantitatively with the precipitin to form the precipitum. What is meant 

 is that measurable amounts of both substances disappear from the superfluid 

 after each interaction. That this is true of the substance contributed by the 

 antiserum we have abundant evidence ; that it is true of the homologous 

 proteid we have no evidence whatever. 



Consistently with our observations, therefore, the results of a precipitin 

 interaction cannot be stated in the form of a simple chemical equation. We 

 are not in a position to formulate any definite hypothesis, but we may at 

 least infer that the processes underlying the interaction are of a more 

 complex nature. From the fact that the homologous proteid is not 

 appreciably diminished, it is suggested that the proteid may exert a catalytic 

 effect on the precipitable substance of the antiserum, whereby a molecular 

 rearrangement is induced and the substance is thrown out of solution. 



Conclusions. 



1. The homologous proteid is not wholly removed from the superfluid of a 

 precipitin interaction, whether it is more than sufficient or less than 

 sufficient to neutralise all the precipitin present. 



2. Conclusive evidence that the homologous proteid is sensibly diminished 

 in similar circumstances has not been obtained. 



3. The substance that is thrown out of solution is derived mainly from 

 the antiserum. 



4. The character of an antiserum depends upon two factors which are 

 mutually independent : (1) the precipitable content ; (2) its precipitability. 



5. The precipitable content is indicated by the maximum precipitum 

 obtainable from a given amount of the antiserum. 



6. Its precipitability is indicated by the minimum amount of homologous 

 proteid that will completely neutralise the precipitin in a given amount of 

 the antiserum. 



7. The solid content of precipitin antisera is increased relatively to that of 

 natural sera. 



