68 THE PROTOZOA 



grains," and so forth bodies which are often mistaken for true 

 cliromatin, but which must be carefully distinguished from it, just 

 as metaplastic bodies are to be distinguished from protoplasm. 

 Among such bodies must be mentioned more especially the so-called 

 " volutin-grains,"* which have attracted much attention of recent 

 years, and which occur in various bacterial or unicellular organisms. 

 The volutin-grains resemble chromatin in showing affinities for 

 so-called " nuclear stains," which they hold more firmly than the 

 chromatin itself, when treated with reagents that extract the stain. 

 According to Reichenow (78), volutin is a nucleic acid combination 

 which is to be regarded as a special reserve-material for the forma- 

 tion of the nucleo-proteins of the chromatin-substance ; during 

 phases of the life-cycle in which the chromatin in the nucleus 

 increases in quantity, the volutin in the cytoplasm diminishes, and, 

 conversely, when the quantity of chromatin is stationary, the 

 volutin-grains increase in number. Volutin-grains are thus seen 

 to be bodies of totally different nature from chromidia, with which 

 they are often confused on account of their similar appearance and 

 staining reactions ; chromidia are formed, typically, as extrusions 

 from the nucleus into the cytoplasm ; volutin-grains, on the other 

 hand, are formed in the cytoplasm, and represent, as it were, a 

 food-substance which is absorbed by the nucleus in the growth and 

 formation of the chromatin. In some cases, however, the meta- 

 chromatinic grains may represent chromidial extrusions from the 

 nucleus which are breaking down or being modified into other 

 substances ; compare, for example, the extrusion of vegetative 

 chromidia, which degenerate into pigment, from the nucleus of 

 Actinosphcerium during a depression-period (p. 209). 



The occurrence in the cell-body of volutin and other substances 

 which resemble chromatin very closely may often render extremely 

 difficult the task of identifying and distinguishing the true chro- 

 matin, especially when it is not concentrated into a definite nucleus, 

 but is scattered in the cytoplasm in the form of chromidial grains. 

 The test upon which reliance is most usually placed for the identi- 

 fication of chromatin is its staining properties, and especially its 

 readiness for combining with basic aniline dyes and certain other 

 colouring matters. But this test is extremely inadequate and un- 

 reliable ; on the one hand, as has been stated above, there are 

 substances, such as volutin, which are coloured by " nuclear " 

 stains more intensely than the true chromatin itself ; on the other 

 hand, in cellular organisms which possess true nuclei containing 

 undoubted chromatin, the staining reactions of the nuclei may be 

 strikingly different in different cases. A good example of each of 



* The name " volutiu " was coined by A. Meyer in 1904, and is derived irom the 

 fact that the substance was first studied by him in Spirillum volutans. 



