Until, however, the cellular nature of the body had been demonstrated, it seemed necessary in some instances to postulate a blastema or exudation to account for certain new formations. But the moment I could show the universality of cells--the moment I could show that bone corpuscles were real cells, and that connective tissues contained cells--from that moment cellular material for the building of new formations was apparent. In fact, the more observers increased the more distinctly was it shown that by far the greater number of new formations arise from the connective tissue. In almost all cases new formations may be seen to be formed by a process of ordinary cell division from previously existing cells. In some cases the cells continue to resemble the parent cells; in other cases they become different. All new formations built of cells which continue true to the parent type we may call homologous new formations; while those which depart from the parent type or undergo degenerative changes we may designate heterologous. In a narrower sense of the word heterologous new formations are alone destructive. The homologous ones may accidentally become very injurious, but still they do not possess what can properly be called a destructive or malignant character. On the other hand, every kind of heterologous formation whenever it has not its seat in entirely superficial parts, has a certain degree of malignity, and even superficial affections, though entirely confined to the most external layers of epidermis, may gradually exercise a very detrimental effect. Indeed, suppuration is of this nature, for suppuration is simply a process of proliferation by means of which cells are produced which do not acquire that degree of consolidation or permanent connection with each other which is necessary for the existence of the body. Pus is not the solvent of cells: but is itself dissolved tissues. A part becomes soft and liquefies, while suppurating, but it is not the pus which causes this softening; on the contrary, it is the pus which is produced as the result of the proliferation of tissues.