ORGANIC SUBSTANCES. 671 
they are therefore supposed to occupy the same position as one 
equivalent of hydrogen in the oil of bitter almonds, or in their 
prototype. The fifth example presents the most remarkable 
circumstance, that the same space which in oil of bitter almonds 
is occupied by 1 equivalent of hydrogen suffices not only for 2 
equivalents of hydrogen, but in addition for 1 equivalent of ni- 
trogen. The mechanical impossibility is no obstacle to this 
theory, and the supporters of metalepsy find no difficulty in re- 
placing an equivalent of hydrogen by 4 atoms or equivalents of 
oxygen and 1 equivalent of nitrogen, or by 2 atoms of oxygen 
and | atom of sulphur. 
It is consequently the most easily applicable of all theories, 
and we need not be surprised that at this moment it is most gene- 
rally adopted for organic combinations ; its author’s well-earned 
celebrity in other ways is no doubt the chief reason for this. 
His treatises since the publication of this theory have mostly 
borne the title of ‘ Memoirs upon the Chemical Types’ (Mé- 
moires sur les Types Chimiques). 
Many more objections could doubtless be raised against this 
theory, but those which we have noticed are sufficient to give an 
idea of the manner in which the metaleptic type-theory considers 
the rational composition of bodies in organic chemistry. 
Simultaneously with Dumas, Laurent worked out the same 
theoretical view, and varied it in an endless manner. The ex- 
traordinary number of new compounds which he had the good 
fortune to discover during his really excellent researches, offered 
him abundant material to test his views upon, and as these re- 
searches were all undertaken for that object, his nomenclature 
has been framed entirely to suit it; thus be has almost forced 
chemists to accept his view of the mode of combination, and 
although during his further progress he has sometimes been 
obliged to alter his mode of conception, he has nevertheless en- 
deavoured to change the views upon inorganic composition to 
suit his own upon organic. The fundamental idea upon which his 
opinions are based is however quite the same as that of Dumas, 
and consists in types and metalepsy. 
The same chemical theme has likewise been varied by Ger- 
hardt in a work upon organic chemistry, in which he allows no 
predecessor to outdo him in setting up fanciful explanations of 
the rational composition of bodies. 
Persoz starts with the fundamental position, that such bodies 
