310 Drs. D. A. Welsh and H. G. Chapman. On the [Apr. 30, 



70° 0. were dense flocculent masses, which settled to form large deposits. 

 Such large deposits were not observed in the neutralised antiserum nor in 

 natural serum at these temperatures. Further experiments on these lines are 

 in progress. 



The Precipitable Content and Precijpitdbility of Antisera. 



When a given amount (say 0"01 gramme) of antiserum is completely 

 neutralised by its homologous proteid, so that no precipitin can be detected 

 in the superfluicl, then no further increase in the amount of homologous 

 proteid will augment the precipitum, and that precipitum may be taken to 

 represent the entire precipitable content of the given amount of that anti- 

 serum. Any reliable method of measuring the precipitum, such as that 

 devised by Nuttall, would afford an indication of the precipitable content of 

 an antiserum, provided that the amount of homologous proteid interacting 

 were sufficient to neutralise all the precipitin within the limits of time 

 allowed. As the complete neutralisation of the precipitin is not taken into 

 consideration, and is not always secured by ISTuttall's original method, we 

 introduced a modification whereby complete neutralisation of the precipitin 

 is secured by interaction with larger amounts of the homologous proteid. 

 The bulk of the precipitate measured in this way affords a datum by 

 means of which the precipitable content of different antisera may be 

 compared. 



Numerous observations serve to show that the precipitum is of a proteid 

 nature, and, in discussing the primary interactions in Experiment I, we 

 indicated another way in which the precipitable content may roughly be 

 expressed — in terms of the amount of proteid to which the maximum 

 precipitum from a given amount of antiserum is approximately equivalent. 

 Thus we saw that the precipitable content of - 01 gramme of the horse anti- 

 serum of Experiment I was O'OOOOa? gramme. The precipitable content of 

 the same amount of the egg antiserum of Experiment III might be similarly 

 represented by a figure of the same order of magnitude. 



Estimated by our modification of ISTuttall's method, the precipitum from 

 - 01 gramme of the horse antiserum of Experiment I, and of the egg anti- 

 serum of Experiment III, measured in each instance O024 c.c. In the 

 common acceptation of the term these antisera would rank as equally 

 "powerful," that is, capable of throwing out of solution equal amounts of 

 their respective homologous proteids. We should prefer to say that the 

 precipitable content of the two antisera was equal. 



Yet there is a striking difference between them, unrevealed by Nuttall's 

 method or by our modification, for the amount of the homologous proteid 



