327 



of antiserum, and that, as the concentration of antiserum 

 increased, the precipitate also tended to increase (12). 1 



In the interactions of ponderable quantities of antigen 

 with antiserum, we have no direct evidence of the amount 

 of antigen present in the precipitate ; but the following 

 facts indicate that it is a quantity small in comparison 

 with that derived from the antiserum. 1. p]ach cubic 

 centimetre of antiserum has a definite precipitable content, 

 and the weight of precipitate is proportional to the weight 

 of antiserum (v. supra). 2. The maximal weight of pre- 

 cipitate from a given amount of antiserum is the same 

 whether it is discharged by a single quantity or by succes- 

 sive smaller quantities of antigen (15). 3. In total inter- 

 actions the weight of precipitate is independent of the 

 weight of antigen (v. supra). 4. In partial interactions 

 the weight of precipitate may be many times greater than 

 the weight of antigen when the quantity of the latter is 



These observations are not inconsistent with the hypo- 

 thesis that antigen and antiserum combine to form the 

 precipitate, but they indicate that it is erroneous to speak 

 of the preeij.it in of t he antiserum precipitating the antigen, 

 in other words, they indicate that the antigen is not the 

 true precipitable substance. 



Arrhenius and Hamburger (20) have brought forward 

 evidence in favour of the interaction taking place between 

 equivalent quantities of antigen and of precipitin. Their 

 experiments do not appeal' to be opposed to ours. They 

 deal rather with another aspect of the question, studied in 

 different experimental conditions. Arrhenius 2 (22) states 



' An interesting corroboration is supplied by Hunter (19), who, work- 



