276 M. Pasteur on Aspartic and Malic Acids. 



ently with the time which is allowed for the treatment of the 

 subject, and without sacrificing that precision of argument which 

 the subject demands. 



The first step towards the solution of a scientific problem is to 

 state it with perspicuity. We shall apply this principle to the 

 one of which we are about to treat. According to the general 

 conception of chemical phsenomena, and it is necessary to take 

 a speculative view of them to be able to arrange them in the form 

 of a science, the substances between which they take place are 

 considered as so many coi'puscular systems of difi"ereDt natures, 

 the constituent molecules of which arc more or less complex. 

 Some of them do not undergo any alteration under the influence 

 of any operations to which they have hitherto been submitted. 

 These belong to that class of substances which are called simple. 

 Others, on the contrary, and they constitute the most numerous 

 class, are capable of being separated by chemical processes into 

 molecular groups of a less complex order, which in their turn 

 are ultimately resolvable into molecules which belong to the 

 class of simple substances. Such molecules as are chemically 

 separable constitute the substances which are called compound. 



In all these systems the constituent corpuscles are individu- 

 ally imperceptible to the senses in consequence of their minute- 

 ness. Nevertheless, with this extreme minuteness, they are con- 

 sidered to possess all the properties of tangible matter. Thus 

 they are assumed to be extended, possessed of figure, and to be 

 themselves composed of parts physically aggregated in various 

 numbers. They are, in short, according to our ideas, so many 

 distinct minute bodies, possessing, like the planets, an attractive 

 force proportional to their mass and reciprocally as the square 

 of their distances, which manifests itself in their weight when 

 they are aggregated in large quantities ; perhaps also they act 

 upon each other at a distance in virtue of forces decreasing more 

 rapidly, which they would exei'cise conjointly with the former, 

 and which we must distinguish from the first-mentioned force by 

 their apparent modes of action, although they might in reality 

 be only complex derivatives of the same general law. The cor- 

 puscles thus defined presei've all their individual properties in 

 the sensible masses foi-med by their aggregation. But con- 

 formably to the conceptions which general physics give us of 

 the conditions under which these aggregates exist, the corpuscles 

 are considered to be always maintained out of mutual contact, 

 either by the repulsive forces which emanate from them, or by 

 the interposition of a medium of inappreciable ponderability, 

 which prevents their actual contact by opposing a resistance to 

 them, or by repelling them. 



These circumstances of condition are common to all the sub- 



