M. Pasteur on Aspartic and Malic Acids. 287 



Three general classes of facts have resulted from this mode of 

 treatment belonging to the three points of view under which the 

 subject was considered. We shall class them in his own man- 

 ner^ indicating for each the proofs on which it rests, and the con- 

 sequences deducible from them. 



1. Optical examination. — The power of rotation which the 

 natural aspartic acid possesses is communicated to all its salts, to 

 the malic acid which is derived from it, and to all the salts of 

 the latter acid. It disappears in the pyrogenous acids. 



This power is null in the artificial aspartic acid, in all the salts 

 of it which have been prepared, in the malic acid derived from 

 it, and all its salts ; neither does it exist in the ulterior pyroge- 

 nous acids derived from it. 



For the sake of brevity, we shall designate these two classes 

 of bodies by the denominations of the active series and the in- 

 active series. The possession or the privation of the powers of 

 rotation which distinguishes between them, proves that, in the 

 corresponding terms of the two series, salts or acids, the consti- 

 tution of their chemical molecules differs, since the members of 

 the one class produce individually an observable influence upon 

 polarized light, which those of the other class do not produce. 



2. Crystallographic examination. — The corresponding bodies 

 of the active and the inactive series, when dissolved in the same 

 medium and placed in parallel circumstances, generally afford 

 crystals differing in form, sometimes very slightly, sometimes 

 altogether incompatible. The fact of incompatibility may with- 

 out doubt be assumed to be owing to accidental circumstances 

 of dimoi-phism. But the constancy with which they are repro- 

 duced within certain correspondent terms of the two series, when 

 all the cii'cumstances are parallel, joined to the invariability of 

 the differences which this same identity of circumstances induces 

 in the other case, suffices, independently of all explanation, to 

 prove that the constituent molecules of the corresponding bodies 

 which are compared together must be differently constituted 

 in the two scries, in conformity to the proposition which the 

 difference of their optical properties had already established. 



3. Chemical examination. — The elementary composition of 

 the corresponding bodies is identical in the two series. Their 

 molecules consist of the same ponderable principles combined 

 in the same atomic proportions. Every operation, which, ap- 

 plied to any one of them, causes fusion, solution, decompo- 

 sition, or combination with other substances, produces similar 

 effects upon its correspondent of the other series, and yields pro- 

 ducts, the composition of which is identical. But M'hilc sup- 

 posing the operation to be always effected comparatively and in 

 parallel circumstances, there are generally differences observed 



