THE WONDERS OF LIFE 



ous and structureless, as we find in many of the protists 

 and many young cells of histona (especially young 

 embryos). But in the great majority of cells the caryo- 

 plasm is divided into two or more different substances, 

 the chief of them being chromatin and achromin. 



The most common division of the caryoplasm in the 

 cells of the animal and plant body, and the one of chief 

 significance for their vital activity, is that into two 

 chemically different substances, which are usually called 

 chromatin (or nuclein) and achromin (or linin). Chro- 

 matin has a greater affinity for coloring (chromos) 

 matter (carmine, haematoxylin, etc.), and so this 

 "colorable nuclear matter" is particularly regarded 

 as the vehicle of heredity. The achromin (or achro- 

 matin, or linin) is either not at all or less easily color- 

 able, and is akin to the cytoplasm; in direct cell-division 

 it enters into close relations with the latter. Achromin 

 is usually found in the form of slender threads, and 

 hence called "nuclear thread-matter" (linin). Chro- 

 matin is generally found in roundish or rod-shaped 

 granules (chromosomata), which exhibit very charac- 

 teristic changes of form (loop formation, etc.) in indirect 

 cell-division. The chemical, physiological, and morpho- 

 logical difference between chromatin and achromin must 

 not be regarded as an original property of cell nuclei (as 

 is wrongly stated sometimes), but is the outcome of a 

 very early phylogenetic differentiation in the originally 

 homogeneous caryoplasm; and this holds also of two 

 other parts of the nucleus — the nucleolus and cen- 

 trosoma. 



In a good many cells, but by no means universally, 

 we find two other constituents of the nucleus, which owe 

 their rise to a further differentiation of the caryoplasm. 

 The nucleolus is a small globular or oval particle, which 

 may be found singly or in numbers in the nucleus, and 

 behaves somewhat differently towards coloring matter 



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