Still other forms of granules have been distinguished in the nucleus by Reinke ('94) and Schloter ('94). Of these the most important are the " cedematin-granules," which according to the first of these authors form the principal mass of the ground-substance or "nuclear sap " of Hertwig and other authors. These granules are identified by both observers with the " cyanophilous granules," which Altmann regarded as the essential elements of the nucleus. It is at present impossible to give a consistent interpretation of the morphological value and physiological relations of these various forms of granules. The most that can be said is that the basichromatin-granules are probably normal structures; that they play a principal role in the life of the nucleus ; that the oxychromatin-granules are nearly related to them ; and that not improbably the one form may be transformed into the other in the manner suggested in Chapter VII.
The nuclear membrane is not yet thoroughly understood, and much discussion has been devoted to the question of its origin and structure. The most probable view is that long since advocated by Klein ('78) and Van. Beneden ('83) that the membrane arises as a condensation of the general protoplasmic reticulum, and is part of the same structure as the linin-network and the cyto-reticulum. Like these, it is in some cases " achromatic," but in other cases it shows the same staining reactions as chromatin, or may be double, consisting of an outer achromatic and an inner chromatic layer. According to Reinke, it consists of oxychromatin-granules like those of the linin-network.
3. Chemistry of the Nucleus The chemical nature of the various nuclear elements will be considered in Chapter VII., and a brief statement will here suffice. The following classification of the nuclear substances, proposed by Schwarz in 1887, has been widely accepted, though open to criticism on various grounds.
3. Paralinin. The ground-substance.
4. Pyrenin or Parachromatin. The inner mass of true nucleoli.
5. Amphipyrenin. The substance of the nuclear membrane.
Chromatin is probably identical with nuclein (p. 24o), which is a compound of nucleic acid (a complex organic acid, rich in phosphorus) and albumin. In certain cases (nuclei of spermatozoa, and probably also the chromosomes at the time of mitosis), chromatin may be composed of nearly pure nucleic acid. The linin is probably composed of plastin," a substance similar to nuclein, but containing a lower percentage of phosphorus, and either belonging to the nucleo-albumins or approaching them. It is nearly related with the substance of the cyto-reticulum. Pyrenin consists of a plastin-substance which stains like linin. Anifthiftyrenin is probably identical with linin, since the nuclear membrane is probably a condensed portion of the general reticulum which forms the boundary between the intra- and extra-nuclear networks. It should be borne in mind, however, that the membrane often has an inner chromatic layer composed of chromatin.