1895. THE NUCLEOLUS. 187 



wonder at the great divergence of opinion upon their nature, both 

 structural and chemical. 



Many great masters in the study of the cell grant a distinction 

 between nuclein-bodies and nucleoli only with the greatest hesitation. 

 Strasburger (1882) in his work, " Ueber die Theilungsvorgange der 

 Zellkerne, etc.," believes that the two bodies are but different stages 

 of development of the same thing. He thinks that as the nuclein- 

 bodies increase in age, they grow, and that with their growth a change 

 in their power of staining takes place, so that they ultimately reach 

 the size and have the properties characteristic of a nucleolus. In a 

 later work (24) Strasburger fully grants a dissimilarity in the 

 substance of nuclein-grains and nucleoli, basing his opinion partly on 

 their relative solubilities in various solvents, and partly on their 

 different behaviour during cell-division. In a yet more recent writing 

 (25) we find Strasburger mentioning the similarity of reaction of 

 nuclein and nucleolus. The same hesitation in the expression of a 

 definite opinion is to be found in Guignard (8) ; he, like Strasburger, 

 believes in the passage of the nuclein-grain into a nucleolus. x\s the 

 former body increases in size it undergoes a chemical change, so that 

 it reacts differently towards colouring fluids at different periods of its 

 existence. According to this theory, therefore, we may meet in the 

 nucleus with nuclein-grains possessed of their distmguishing reactions; 

 we may meet also, side by side with these, with other grains, the 

 chemical behaviour of which is dissimilar from that presented by 

 nuclein, and yet different from that of the nucleolus ; and we may 

 meet besides with yet other grains, larger in size, and different in 

 chemical properties from either of the two former ones, which are 

 stamped by their peculiarities as veritable nucleoli ; and all these 

 three things (and under the second heading may be included many 

 varieties) are but phases of one and the same body. 



Flemming (7) sees a radical difference between nucleoli and 

 nuclein-bodies ; so also Pfitzner (18), who studied the nuclei of 

 Hydra. Juranyi (14), on the other hand, regards the nucleoli as 

 thickened parts of the nuclear threadwork, and hence as consisting of 

 nuclein. 



Schmitz (20) not only classes nucleoli and chromatin-grains 

 together, but includes in the same category the pyrenoids, those 

 curious bodies with a still obscure function which are met with in the 

 chromatophores of many Alga;. The grounds for this belief seem, 

 however, to be insufficient to bear it out. Zacharias has shown that 

 there is a certain similarity between nucleoli and pyrenoids, but that 

 it is not a close one, and that, moreover, both these bodies are sharply 

 distinguished from nuclein. 



In 1881 Zacharias published the first of his series of articles on 

 the micro-chemistry of the cell ; they have appeared in the Botanische 

 Zettung, and their value can be best expressed by saying that they 

 are among the most important contents of a periodical in the pages of 



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