288 M. Pasteur on Aspartic and Malic Acids. 



in the details of its action and in its effects. Such, for example, 

 are the differences, frequeiatly slight, but nevertheless constant 

 and appreciable, in the fusibility, the solubility, or the time ne- 

 cessary for the accomplishment of certain transformations, as if 

 there existed between the molecules of the bodies compared a 

 relative aptitude of greater or less extent to assume simultane- 

 ously this or that state. Thus when crystals of active and in- 

 active malic acids, which are completely isomeric, are placed 

 together in a moist atmosphere, the ciystals of the inactive acid 

 absorb during two or three hours the very small quantity of water 

 which they are capable of taking up, after which their weight does 

 not suffer any further change. The active crystals, on the con- 

 trary, absorb water slowly and progressively until they are con- 

 verted into a viscous liquid. The compounds of active and inactive 

 aspartic acidwith hydrochloric acid present the same difference in 

 a more decisive manner. The active and inactive malates of lead, 

 when precipitated from their respective solutions, are amorphous, 

 and after a certain time both assume the form of acicular cry- 

 stals. But in circumstances in every respect parallel, the time 

 which the active malate requires for this change is frequently 

 only a few hours, while for the inactive malate it is frequently 

 several days. All the correspondent products of these two series 

 evince similar differences in what may be called their individual 

 disposition. Discrepancies of this nature are considered as un- 

 important in the ordinaiy course of chemical operations ; and 

 there is perhaps frequently sufficient reason for their being dis- 

 regarded as being dependent upon physical accidents uncon- 

 nected with the molecular constitution, and as being too minute 

 to be considered as essential characters. But in the two series 

 of bodies, active and inactive, which M. Pasteur has studied, 

 these feeble inequalities acquire an entirely different importance ; 

 for they there become the sensible indications, and the natural 

 consequences of the difference in the molecular constitution of 

 the corresponding bodies of those two series which had already 

 been made known by the optical and crystallographical tests. 



M. Pasteur justly remarks, that an example of isomerism is 

 here presented as complicated as, and at the same time more con- 

 sistent, more extended than, any which have hitherto been ob- 

 served in chemistry, great as is their number. The constant 

 identity of the effects which the same reactions produce on the cor- 

 responding terms of the two sei'ies, affords him strong reasons for 

 presuming, that if it were possible to produce active asparagine 

 from active aspartic acid in a similar but inverse manner to that 

 in which the acid is derived from the asparagine, a parallel pro- 

 cess applied to the inactive aspartic acid would give an inactive 

 asparagine also isomeric with the natural. The same analogical 



