ORGANIC GROUPS AND SERIES. 47 



known as the aromatic class and the fatty class, and exemplified in 

 the accompanying lists : 



Fatty Acids Aromatic Acids 



Formic C H 3 O z Collie ? C 6 H 4 O a 



Acetic C a H 4 O z Benzoic C 7 H 6 O a 



Propionic C 3 H 6 O a Toluic C 8 H 8 0, 



Butyric C 4 H 8 O a Picic C 9 H I0 8 



Valeric C 5 H I0 2 Cuminic C IO H Ia O a 



Melissic C 30 H 6o O a 



The acids of these two series presented, I told you, a marked 

 parallelism in their constitution, seriation, and properties ; and, 

 moreover, when submitted to the action of the same chemical 

 reagents, underwent precisely analogous metamorphoses. I dwelt 

 still more upon the mutual resemblance manifested by consecu- 

 tive members of the same series, and pointed out that even the 

 most remote members were distinguished from one another by 

 gradational differences only. I observed, also, that each one of 

 these primary monobasic acids> fatty or aromatic, was associated 

 with a more or less complete set of congeners, which differed 

 from it in constitution and properties, but were correlated with it 

 by the circumstance of their containing the same number of 

 carbon atoms, and still more markedly by their derivation from, 

 and convertibility into it and one another that acetic acid 

 C 2 H 4 2 , for instance, was associated with the less oxidised bodies, 

 olefiant gas C 2 H 4 , alcohol C 2 H6O, and aldehyd C 2 H 4 0, as well as 

 with the more highly oxidised glycolic and oxalic acids, C 2 H 4 3 

 and C 2 H 2 4 , respectively to such an extent, indeed, that they 

 might all be regarded as varieties of one and the same primitive 

 molecule. I further went on to say that the complex tissue pro- 

 ducts of the animal and vegetable kingdoms were built up of the 

 residues of these fatty and aromatic acids, and of their respective 

 congeners ; so that, upon breaking up such tissue products into 

 their constituent molecules, we were, in the great majority of 

 instances, able, even at the present time, to refer the constituent 



