"In developing his ideas of nuclei which were used as a basis of classification in Gmelin's large Handbook of Chemistry [Handbuch der Chemie], as well as in his own Chemical Method, and in his theory of types, he introduced to science the words "anhydride," "amide," "imide," "amidic acid," and others. His Theory of Nuclei was originally mentioned in his Inaugural Dissertation at the Faculté des Sciences at Paris in 1837, but it must not be forgotten that these doctrines are also associated with the name of Gerhardt, who has a share in the honour of their conception and introduction. The Nucleus Theory amounted to this:—The molecules of organic bodies, he said, are either nuclei, or compounds of nuclei, with other substances placed outside them. These nuclei are groups of carbon atoms united with other elements, and are either (1) fundamental nuclei, consisting of carbon and hydrogen only, or (2) derivative nuclei, derived from the fundamental nuclei by substitution. The bodies substituted are generally chlorine, bromine, iodine, oxygen, or nitrogen, but compound bodies, acting as radicles, may be in like manner substituted for hydrogen and enter into the nucleus... In constructing his nuclei and comparing them to prisms, he abandoned the dualistic system, and viewed the compound as a single unitary whole like a crystal. Although the Nucleus Theory has not survived, it laid the foundation of the theory of types which we still use."