42 THE CELL 



composed, albumen and nitrogenous bases being formed, whilst in 

 addition phosphoric acid separates out. The two latter decom- 

 position products are also formed from nucleic acid. The bases 

 are: adenin, hypoxanthin, guanin, and xanthin." 



PARANUCLEIN, or pyrenin, is a proteid substance, which is always 

 present in the nucleus ; however, the part it plays in the vital 

 functions of the latter has not yet been worked out, much less being 

 known about it than about nuclein. It occurs in the nucleus in 

 the form of small granules, which are described as true nucleoli 

 or nuclear corpuscles (Fig. 20). 



These paranuclein bodies resist the action of all the media 

 (distilled water, very dilute alkaline solutions, solutions of salt, 

 sulphate of magnesia, potassium phosphate, lime-water) in which 

 nuclein substances swell up. Whilst the latter disappear from 

 view in the nuclear cavity, which has become homogeneous in 

 appearance, the former often stand out with greater clearness. 

 They are invariably more easily seen after death than during life. 



This explains the fact that these nuclear corpuscles were well 

 known long ago to the older histologists, Schleiden and Schwann, 

 who always examined their tissues in water. 



Osmic acid is a very useful reagent for rendering these corpuscles 

 visible, for it very much increases their refractive power, whilst 

 rendering the nuclein structures paler. 



Paranuclein and nuclein behave quite differently towards acetic 

 acid (1 to 50 per cent.). Whilst the latter coagulates, and in- 

 creases in refractive power, the nuclear corpuscles swell up more 

 or less, and may become quite transparent ; however, they do not 

 become dissolved, for if the acetic acid is washed away, they 

 shrink up, and become visible again. 



In addition, it must be pointed out that paranuclein, in 

 contradistinction to nuclein, is insoluble in 20 per cent, solution 

 of common salt, in a saturated solution of sulphate of magnesia, 

 in 1 per cent, and 5 per cent, solutions of potassium phosphate, 

 of ferrocyanide of potassium plus acetic acid, and of copper 

 sulphate ; finally, it is very resistent to the action of the pan- 

 creatic juice. 



Further distinct differences are shown in their behaviour to- 

 wards staining solutions. As Zacharias has observed, and as I can 

 corroborate as a general rule from my own experience, nuclein 

 bodies become especially clearly and intensely coloured in acid 

 staining solutions (aceto-carmine, methyl green, and acetic acid), 



