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shape of the nucleus is only one of the methods of indicating the vibration or oscillation which was first proposed by Kekul6 for the benzene structure, a n d is of interest now in another connection. These formulas represent all the possible structures produced b y the making and breaking of bonds, each make and break causing a definite absorption band. This conception of make arid break hi,tuwn the atoms in the molecule being responsible for the a1)sorption l ~ a n t l sis not lar removed from the physicist’s conception of tlie tnotion of tlie electron within tlie a t o m or molecule being responsible for the optical phenotnena. In Appendix A , the R e h t ion., o j . V / m ~ o c h i ~i)si/ir j , io Ijhj~.riologyare discussed briefly, and in Appendix 13, directions ;ire given for tlie construction of stereochemical models. This book is fully up t o the best of the other volumes of the series, a n d is indispensable to every organic cliemist. Exception may be taken t o the statement on page 41 t h a t the solid racemic compound possesses a molecular weight double t h a t of one active component, \vhen as a rnatter of fact, practically nothing is known of the molecular weight of any substance in the solid state. The proof-reading has been well done, very few misprints being noticeable, the most serious being on page 14, where t h e length of t h e liquid layer for the specific rotation is given a s centimeters instcad of deciiiietc.rs. The expression is given correctly in the foot-note on page 1 2 - 7 . I
