In these we include the changes which occur in the proper substance of the tissues, the structures which perform the special functions of the parts. We have the numerous epithelial structures forming the secreting substance of glands, and we have the parenchyma of nerve tissue, of muscle, of bone, of the lungs, etc.

In many acute inflammations the only obvious changes apart from the blood-vessels are degenerative, consisting mainly of necrosis and fatty degeneration. In many other cases, however, there are active changes visible in the parenchymatous cells, although it is also true that these are often associated with degenerative changes.

The active parenchymatous changes consist mainly of enlargement of the protoplasm, due to an infiltration with albuminous material. The cells acquire in consequence a granular clouded appearance, which is expressed in the name Cloudy swelling. (See under Albuminous Infiltration.) At the same time the cells frequently multiply, and they do this by the process of karyomitosis. The new-formed cells frequently depart from their position, especially in inflammations of epithelium. This process of Desquamation causes the cells to form sometimes a material part of exudations. (See above.) These phenomena of cloudy swelling and desquamation are frequently associated with Fatty degeneration. Another occasional sign of increased activity is an increase in the secretion of glands involved in inflammations. Thus the secretion of mucus is frequently increased in inflammations involving mucous membranes.

There are some inflammations in which these phenomena are so characteristic that Virchow's name of Parenchymatous inflammation is properly used for them. It may be presumed that the irritant in these cases, usually a morbid poison, has special affinities for the parenchymatous structures. It is not to be inferred, however, that the phenomena in the blood-vessels already described are absent. They are probably present in all cases, and they may be much more prominent during life than one would infer from the appearances after death.