1895. THE NUCLEOLUS. 189 



of the nucleolus which digestive fluids abstract ; the digestive-remnant 

 and the nuclein-grains of the nucleus are left unstained. Alkaline 

 solutions of carmine colour the nucleoli rapidly and deeply, but act 

 on nuclein only slowly and never very intensely. Acid carmine 

 solutions have precisely the opposite effects, being especially nuclein 

 stains with little action on nucleoli. This behaviour with different 

 carmine solutions again points to the two-fold structure of the body 

 in question, and to the entire absence of nuclein from it. 



In direct contradiction to these views Schwartz (22) asserts that 

 the nucleolus consists of a single substance — pyrenin, .which has a 

 close chemical resemblance to the material composing the wall of 

 the nucleus, and which he accordingly names " amphipyrenin." 

 This pyrenin exists, he says, in two modifications, the soluble and 

 the insoluble forms, the former being found in young nucleoli, the 

 latter in those which are older ; but what is to be clearly borne in 

 mind is that both forms are chemically similar, and hence to be 

 included under the single name of pyrenin. He has studied the 

 action of different reagents upon the nucleolus most carefully and 

 patiently ; but invaluable as his results are, it would be out of the 

 question to enter into their details here. It may be mentioned, 

 however, that they frequently are at variance with those of 

 Zacharias ; for instance, Schwartz believes it to be extremely 

 probable that the substance of the nucleolus is in itself soluble in 

 water (in contradiction to Zacharias), but that upon the injury of the 

 cell in examination, the penetration of acid substances or tannins 

 contained in the cell-sap of the protoplasm fixes and renders the 

 nucleolar substances insoluble. He fully bears out Zacharias in 

 the opinion that nucleoli are entirely dissimilar from chromatin- 

 grains. 



Another interesting point connected with the nucleolus is the 

 change which this undergoes with increasing age. We are very largely 

 indebted to Johow (13) for^information in this respect. There seems 

 to be a decrease in size, and often an entire disappearance of the 

 nucleolus in older cells ; moreover, in cells which no longer under- 

 go division, the nucleolus exhibits slow changes of form, more or less 

 amoeboid in nature {e.g., cells of Cham), the pseudopodial processes 

 becoming separated from the main body of the nucleolus, and 

 drawing themselves together as a number of disconnected granules, 

 still giving the ordinary nucleolar reactions. 



In what has already been said it will be seen that there is much 

 which is uncertain and undetermined ; but there yet remains a 

 question to be dealt with which surpasses all else in point of in- 

 decision and variety of opinion. This is the inquiry into the fate of 

 the nucleolus during cell-division. 



The only point as to which there is a consensus of opinion is that 

 the nucleolus, at the time of activity, disappears. What becomes of 

 it? Which, if any, of the new structures appearing in the nucleus 



