M. Pasteur on Aspartic and Malic Acids. 291 



the four isomeric products of cyanogen ; for the capacities of satu- 

 ration of the comparative terms are always found to be exactly 

 equal, while in the products of cyanogen they are unequal, and 

 graduate among each other in simple relations, in which the 

 masses of the constituent corpuscles participate. There remain, 

 thei-efore, only the two other causes of dissimilarity which can be 

 assumed ; the diversity of configuration, and that of arrangement, 

 either individually or conjointly. Now here is presented an 

 extremely favourable opportunity of studying their effects with 

 regard to the former, the possibility of tracing it through an 

 infinite variety of combinations, all of which are definite, and 

 nearly all crystallizable ; and if this examination should not 

 ultimately lead to their distinction one from the other, it would 

 always be possible to distinguish the characters which appertain 

 to them, together or separately. Such are the important advan- 

 tages which have not hitherto been offered by any other chemical 

 problem ; and we expect of M. Pasteur that he will not fail to 

 follow it up throughout the entire extent of its consequences. 



Another investigation, far less difficult, may now become very 

 rich in results for him and all those who may be desirous of en- 

 tering upon this study. The number of vegetable acids in which 

 the power of rotation has hitherto been observed is very limited. 

 They are the dextrotartaric and levotartaric, their derivative tar- 

 tarovinic and tartaromethyhc acids ; the camphoric, camphoramic, 

 aspartic, malic and kinic. It is extremely probable that others 

 will be found ]30ssessing, like these, the same power, if they are 

 sought for in the juices of plants collected at different periods of 

 their growth, and in juices of fruits expressed at different stages 

 of their maturation. These would have but little interest if it 

 were only possible to expect isolated results, which could only 

 add one more to this class of bodies so remarkable for their in- 

 stability. But the presence of the rotatory power in those acids 

 which possess it gives them an entirely different value ; for by 

 tracing the modifications of this power in their salts, their others, 

 their chemical derivatives, and all the combinations whatever 

 into which they can be made to enter, chemistiy, crystallo- 

 graphy and molecular optics would thus acquire an abundance of 

 new facts, by which each science would be enriched and its 

 range of view extended. The experimental sciences would be 

 improved by a more true appreciation of already known results, 

 and by the discovery of new facts which would extend their field 

 of application. We point out immediately the first kind of ser- 

 vices in the perseverance of M. Pasteur. AVc now recommend 

 the second to his zeal, and to that of all experimentalists who 

 are capable of joining with liim in tliis study ; for there is a suffi- 

 cient occupation for every one. 



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