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Scientific Proceedings (44). 
to the lower zone precipitate only. A solution of the precipitate 
by this method gives a perfectly clear solution which fixes as well 
as the formed precipitate. In similar manner solution of the 
precipitate by traces of acid or of alkali gives a fixing fluid equal 
in potency to the undissolved precipitate; the latter method is, 
for technical reasons, less conclusive than the former method of 
solution. 
The conclusion to be drawn from this work is that alexin 
fixation by a mixture of serum and antiserum is produced by an 
antigen-antibody complex distinct from precipitinogen-precipitin 
but usually brought down by the precipitate in its formation in 
such a way as to give the appearance that the fixation is produced 
by the precipitate itself. It would seem then that Gengou's 
original supposition, without direct proof, of anti-albuminous 
sensitizers more correctly explains this type of the fixation reaction. 
The best expression of the conditions as they seem to exist would 
be found, however, in Nicolle's hypothesis who concludes that 
antisera contain two classes of antibodies, "coagulins" and 
"lysins," the former, in this particular instance, producing pre- 
cipitation, and the latter, the fixation reaction. 
