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Proceedings of the Royal Society of Edinburgh. [Sess. 
a good reaction, large clumps in a perfectly clear fluid, readily visible with 
the two-thirds lens or, indeed, the unaided eye, would be produced by a low 
dilution of the serum — 1 : 10 or 1 : 20. Very often, even at this stage, the 
macroscopical reaction in the sedimentation tube was absent. Next, the 
microscopical reaction would often disappear for a day or two, or even 
longer ; finally, it would become firmly established, and obtainable in the 
majority of cases in considerably higher dilutions, and the micro- and 
macroscopical reactions would control and confirm each other with absolute 
precision. The exigencies of experiment, necessitating the destruction of 
