280 M. Pasteur on Aspartic and Malic Acids. 



reaction. Then mentally tracing back the actions of those 

 groups to the inv-isible coi-puscles which compose them, it has 

 become possible, justlj'^ and without hypothesis, to characterize 

 these individually in each substance by the triple conjunction of 

 their observed properties, with the nature and the relative pro- 

 portion of the ponderable ingredients of which they are com- 

 posed. 



The science of chemistry has arrived at these abstract prin- 

 ciples which appear to be unattainable in two distinct ways, that 

 of coordination and that of speculation. In the former of these, 

 chemistry relied solely upon its own capabilities, and did not 

 extend its contemplations beyond the immediate results of ex- 

 periment. Thus was analysis brought to a state of perfection, 

 the law of multiple proportions discovered, and the calculation of 

 equivalents invented. This calculation has been to chemistry the 

 principle of all generalization. For in the first place, by defi- 

 ning the results of analyses no longer according to their nume- 

 rical details, which leave them isolated, but by the relative 

 masses of the different simple ingredients which constitute each 

 substance, it has rendered evident one of the principal mecha- 

 nical conditions of their individual existence which it has been 

 possible to express generally by means of a literal notation of 

 extreme simplicity. Then as the law of multiple proportions 

 was naturally realized in those expressions, all the substances 

 analysed have been symbolically represented by the association 

 of two characters ; the one specifying the particular nature of 

 each ingredient, the other stating the multiple resulting from 

 its conventional unity which enters into each substance under 

 consideration. 



These two characters comprise all the data which direct ana- 

 lysis is capable of affording. But after the exposition which we 

 have given of the chemical problem, their reunion would be in- 

 sufficient to establish a complete definition ; for they do not 

 define the relations of mass which there may be between the 

 corpuscles constituting different substances ; they do not express 

 anything which may have a relation to the particular configura- 

 tions of those corpuscles ; nor further, what is the internal distri- 

 bution of the different ingredients of which they are composed. 

 Now these are so many determining peculiarities of the actions 

 exercised by the corpuscles. Thus a number of substances have 

 been met with, which, although consisting of the same element- 

 ary bodies united in the same proportions, possess physical and 

 chemical properties very different. These substances are called 

 isomeric. It was from that time necessary to search elsewhere 

 than in the results of direct analysis for general characters of 

 identity or of difference, which might be annexed to the symbolic 



