64 INTRODUCTION TO CYTOLOGY 



of this membrane has been a subject of much controversy. Some have 

 regarded it as a precipitation membrane laid down when the newly 

 formed karyolymph comes in contact with the cytoplasm at the time the 

 daughter nuclei are reconstructed during the closing phases of mitosis, 

 while others (Lawson 1903) have interpreted it as merely a denser limit- 

 ing layer of the -cytoplasm. The above cited work of Kite and Chambers, 

 however, leaves no doubt that the membrane is a definite morphological 

 structure belonging to the nucleus: although it is at times very delicate, 

 it remains intact when the nucleus is pushed and pulled about by the 

 dissecting instrument, and is thrown into folds when the karyolymph is 

 withdrawn with a pipette. 



Within the nuclear membrane is a series of gels of varying consistency. 

 The nuclear sap, or karyolymph, is a highly transparent substance which 

 is generally looked upon as homogeneous, although it has been thought 

 by some workers (Reinke 1894) to be made up of large, pale "cedamatin 

 granules." It may be in the sol or gel state. Imbedded in the karyo- 

 lymph is a network or reticulum, which may be relatively uniform through- 

 out the nucleus or only fragmentary and incomplete. It is usually said 

 to be composed of a gel substance known as achromatin (Flemming 1879) 

 or linin (Schwarz 1887). Supported on the linin reticulum is the chroma- 

 tin (Flemming 1879). This highly stainable substance may exist in the 

 form of small granules or droplets at the nodes of the reticulum, or 

 apparently in many nuclei as a fluid thin enough to distribute itself more 

 or less uniformly throughout the achromatic substance. In the latter 

 case the whole reticulum appears to be composed of a single unevenly 

 stained material, careful examination showing the " chromatic granules' 1 

 and " achromatic support " to be its thicker and finer portions respectively 

 (Fig. 51) (Gregoire and Wyagerts 1903; Gregoire 1906; Sharp 1913, 

 1920). According to Kite (1913) the granules in the living nucleus con- 

 sist of a very concentrated gel, the supporting reticulum of a somewhat 

 more dilute but not at all fibrous gel, and the karyolymph of a gel which 

 is the most dilute of all. 



Heidenhain (1894) found imbedded in the colorless linin net two sorts 

 of chromatin in the form of granules: oxychromatin, consisting largely of 

 plastin, poor in phosphorus, and staining with the acid dyes; and basi- 

 chromatin, composed mainly of nuclein, rich in phosphorus, and staining 

 with the basic dyes. These two forms of chromatin apparently may 

 change into each other by the addition or loss of phosphorus. The peri- 

 odic changes in the staining reactions of many nuclei therefore indicate 

 changes in the chemical composition of the chromatin, and these in turn 

 point to the intimate association of the nucleus with the periodic physi- 

 ological processes of the cell. As used by many writers the term oxy- 

 chromatin includes also the linin, so that in much cytological literature 

 linin and oxychromatin are more or less interchangeable terms, while 



