THE CAUSES OF DIFFERENTIAL DYEING 101 



feature is the strong colouring of chromatin. Metaphase and 

 anaphase chromosomes, both mitotic and meiotic, are more 

 deeply coloured than anything else; nuclei are conspicuous on 

 account of their chromatin content. The mucous secretion of the 

 goblet-cells in the intestine may be rather strongly dyed, fre- 

 quently in a different colour from anything else (p. 105). The 

 cytoplasm of most kinds of cells (such as spermatogonia and 

 spermatocytes, and the interstitial cells of the testis) is scarcely 

 tinged. Certain kinds of cells, however, have a large amount of 

 ribonucleic acid in the cytoplasm, and this takes the dye. The 

 epithelial cells of the crypts of Lieberkiihn are examples; the 

 bases of the exocrine cells of the pancreas are even more strongly 

 dyed, because of the particularly great amount of ribonucleic 

 acid associated with the massive endoplasmic reticulum of this 

 region. There is scarcely any colour, however, in the contractile 

 substance of smooth muscle, in collagen fibres, in the free border 

 of the intestinal epithelium, or in the large granules of the Paneth 

 cells in the crypts of Lieberkiihn. There is nothing to distinguish 

 the granules of the eosinophil leucocytes in the cores of the 

 intestinal villi, and these cells can scarcely be recognized. Red 

 blood-corpuscles are not dyed. 



The whole aspect of sections of the same tissues coloured with 

 a typical anionic dye is entirely different. There is a general 

 colouring of the cytoplasm of most kinds of cells. The cytoplasm 

 of the interstitial cells of the testis takes up more of the dye than 

 that of the spermatogenetic cells, and groups of the former kind 

 of cells therefore stand out rather prominently under the low 

 power of the microscope. The basal part of the exocrine cells of 

 the pancreas is moderately deeply coloured. The cytoplasm of 

 the epithelium of the crypts is pale. The contractile substance of 

 smooth muscle takes the dye; so do collagen fibres. None of 

 these tissue-constituents, however, is nearly so strongly coloured 

 as certain cytoplasmic granules, namely those of the Paneth cells 

 and particularly the minute ones of the eosinophil leucocytes in 

 the cores of the villi. Chromatin shows no special affinity for the 

 dye and is only lightly coloured. The nuclear sap is colourless. 

 The nuclei therefore often appear almost as though they were 



