40 THE CELL 



b. Nuclear Substance. As regards its composition, the 

 nucleus is a fairly fixed body. Two chemically distinct proteid 

 substances, which can be distinguished from one another with the 

 microscope, are always present ; very often there are more. The 

 two constant ones are nuclein or chromatin, and paranuclein, or 

 pyrenin ; in addition, linin, nuclear sap, and amphipyrenin are 

 generally to be found. 



Of these, nuclein, or chromatin, is the most characteristic pro- 

 teid of the nucleus, and it generally preponderates as regards 

 quantity. When fresh it resembles non-granular protoplasm 

 (hyaloplasm), but it can be easily distinguished from this substance 

 by its behaviour towards certain staining solutions. After it has 

 been caused to coagulate by means of reagents, it takes up the 

 colouring matter from suitably prepared staining solutions (solu- 

 tions of carmine, hsematoxylin, aniline dyes), as has been discovered 

 by Grerlach. This occurs to a more considerable extent during the 

 stages preceding division, and during division itself, than when the 

 nucleus is in a resting condition. Whether this is due to chemical 

 or to physical causes has not yet been worked out. The art of 

 staining is now so fully understood that it is quite easy to make 

 the nuclein of the nucleus stand out clearly from the rest of the 

 nucleus and the protoplasm, which are either quite colourless or 

 are only slightly stained. In this manner even small particles of 

 nuclein, only about as large as Bacteria, may be rendered visible 

 in comparatively speaking large masses of protoplasm, as, for 

 example, the minute heads of spermatozoa, or the chromosomes of 

 the direction spindles in the centres of large egg-cells. 



The following fact, which is emphasised by Fol (II. 13), may at 

 some future period prove to be of far-reaching importance : " that 

 the staining of the nucleus with neutral staining solutions always 

 produces the same shade of colour as the dye in question assumes 

 when a small quantity of a substance of basic reaction is added to 

 it. For example, red alum carmine becomes lilac when the solu- 

 tion is rendered slightly alkaline, Bohmer's violet hematoxylin 

 becomes blue, red ribesia (black currant juice) bluish-green, whilst 

 the red dye made from red cabbage turns green. Now, it has been 

 observed that nuclei of tissue-cells, stained with neutral solutions 

 of these substances, exhibit a corresponding colouration ; that is to 

 say, they become lilac in alum carmine, blue in hsematoxylin, light 

 blue in ribesia, green in the colouring matter of red cabbage. 

 That part of the nucleus which can be stained {the nuclein) behaves, 



