The illustrations are also compiled from various sources. These are mentioned underneath each figure. The illustra tions of apparatus not so mentioned have been drawn from my own sketches. For those Of the osazone crystals, haemin, and tyrosine, I am indebted to Miss V. G. Sheffield, who has also kindly helped in reading the proof sheets. In most physiological chemistry laboratories the strengths Of the reagents employed are very various, e.g. Dilute acetic acid may be I per cent, or 2 per cent., or 5 per cent, or even IO per cent. In order that all workers may employ a reagent of standard concentration, a list Of reagents has been carefully drawn up and is appended.
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