92 GENERAL PHYSIOLOGY 



Recently, Zacharias ('81-'87) and Frank Schwarz ('87) have en- 

 deavoured to replace the customary names of the individual sub- 

 stances by other names. Thus, the chromatic substance has been 

 termed nuclein, the achromatic substance linin, the nucleolar 

 substance paranuclein or pyrenin, the nuclear sap paralinin, and 

 the substance of the nuclear membrane amphipyrenin. The 

 adoption of these names is not recommended, for they may 

 so easily be confounded with chemical notions as to lead to the 

 error of seeming to deal with chemical entities, while the nuclear 

 substances in question are purely morphological. If the term 

 nuclein were to be employed in a chemical sense, the chromatic 

 nuclear substance would be placed in a chemical contrast with the 

 other nuclear substances that does not really exist, for the majority 

 of other nuclear substances likewise belong chemically to the so- 

 called nucleins, representing different kinds of the latter. There- 

 fore it is more fitting to employ the original names above mentioned 

 for the morphological nuclear constituents, and not to confuse the 

 latter with chemical substances. 



One more phenomenon relative to the differentiations of the 

 individual substances is of interest. This is the fact that, of the 

 substances that occur together within the nucleus in most cells, 

 some have become differentiated in many cells into separate masses 

 within the protoplasm, so that two entirely different forms of 

 nucleus occur side by side within the same cell. This condition is 

 almost universally realised in ciliate Infusoria, which possess, in 

 addition to a larger nucleus, the macronucleus, which in some 

 species and at certain periods seems to consist chiefly of chromatic 

 substance, one, several, or often a great number of the so-called 

 accessory nuclei, or micronuclei, which likewise in some species 

 and at certain periods seem to consist mostly of achromatic sub- 

 stance. The claim of the two elements in the infusorian cell to be 

 regarded as two different nuclear substances is based upon the 

 phenomena which, according to the striking investigations of R. 

 Hertwig ('88-'89), appear in the conjugation of two individuals. 

 Here the chief nucleus goes to pieces completely in the protoplasm, 

 and after conjugation a new rudiment of it is differentiated from 

 the substance of the accessory nuclei. While in the ciliate 

 Infusoria the two forms of nucleus remain throughout life, in 

 the Difflugice of the PJiizopoda a localised differentiation of two 

 nuclei appears only during the period of conjugation and gives 

 place afterwards to the uninucleated condition. 1 



c. The Structure of the Nucleus 



It has been seen that the achromatic substance forms in the 

 ground-mass of the granular nuclear sap a supporting-structure, in 



1 Cf. Verworn ('90, 1). 



