284 M. Pasteur on Aspartic and Malic Acids. 



polarized light iu the actual state in which they are observed. 

 Up to the present time, this power is, next to that of gravitation, 

 the only observable character which it is possible to apply to them 

 individually. There is therefore a strong reason for adhering to 

 it in the first instance, and to prefer the investigation of those 

 combinations in which its presence is capable of serving as a 

 guide. Now these are at once the most diversified, and those 

 whose constitution it is most difficult to explain decisively from 

 merely chemical indications, by reason of their instability, joined 

 to the feebleness and frequent indistinctness of their reactions. 



The novel and valuable series of researches which M. Pastern- 

 has pursued during the last foui* years with a success worthy of 

 his perseverance, confirms all the arguments w^hich we have just 

 stated. These researches have been conducted so as to unite the 

 ap^Dliances of crystallography, chemistry, and molecular optics. 

 In these reside both the principle and the condition of success. 

 In fact, by the suppression of one term of that conjunction, no 

 matter which, the two others, either united or separately, could 

 not have done more than furnish to the most sagacious minds 

 isolated and scattered results, between which that connexion, 

 which at the present time constitutes their principal value, 

 would be entirely overlooked, and each of which would be of 

 no further importance than as being a fact of detail added to 

 those previously known. But by this happy union of all the 

 experimental methods, by means of which the field of investi- 

 gation upon which M. Pasteur has entered could be explored, 

 the Avhole series of phajnomena which he studied revealed them- 

 selves to him. Not only has the racemic acid, which was hitherto 

 supposed to be an homogeneous substance, been separated into 

 two other acids molccularly difi'erent, possessing equal and con- 

 trary powers of rotation ; but further, the crystallographic cha- 

 racters, by which those compounds are distinguished from the 

 neuti'al system which their combination affords, have been inves- 

 tigated, traced and established, not only in the bodies themselves, 

 but also throughout the whole range of their crystallizable salts. 

 These characters have been subsequently detected in numerous 

 other organic products, which possess or are destitute of the 

 power of rotation ; they have become the indications, not yet 

 universallj'^, but very frequently presented by these two states. 

 Thus has been seen for the first time the manifestation of obser- 

 vable relations between the natural properties of the imperceptible 

 molecules of which bodies are composed, and the configuration 

 of the sensible masses which results from the aggregation of these 

 molecules in crystals. 



The recent memoir which M. Pasteur has just submitted to 

 your notice, and of which we arc now about to render an account, 



