362 



SCIENCE. 



[N. S. Vol. XII. No. 297. 



multiplied, it was seen that numerous ele- 

 mentary particles, which were obviously in 

 their nature cells, did not possess an en- 

 closing envelope. A wall ceased to have a 

 primary value as a constituent part of a 

 cell, the necessary vesicular character of 

 which therefore could no longer be enter- 

 tained. 



The other constituent parts of a cell are 

 the cell plasm, which forms the body of the 

 cell, and the nucleus imbedded in its sub- 

 stance. Notwithstanding the very minute 

 size of the nucleus, which even in the 

 largest cells is not more than -g-^oth inch 

 in diameter, and usually is considerably 

 smaller, its almost constant form, its well- 

 defined sharp outline, and its power of re- 

 sisting the action of strong reagents when 

 applied to the cell, have from the period of 

 its discovery by Eobert Brown caused his- 

 tologists to bestow on it much attention. 

 Its structure and chemical composition ; its 

 mode of origin ; the part which it plays in 

 the formation of new cells, and its function 

 in nutrition and secretion have been in- 

 vestigated. 



When examined under favorable con- 

 ditions in its passive or resting state, the 

 nucleus is seen to be bounded by a mem- 

 brane which separates it from the cell 

 plasm and gives it the characteristic sharp 

 contour. It contains an apparently struc- 

 tureless nuclear substance, nucleoplasm or 

 enchylema, in which are embedded one or 

 more extremely minute particles called 

 nucleoli, along with a network of exceed- 

 ingly fine threads or fibers, which in the 

 active living cell play an essential part in 

 the production of new nuclei within the 

 cell. In its chemical composition the nu- 

 clear substance consists of albuminous plas- 

 tin and globulin ; and of a special material 

 named nuclein, rich in phosphorus and with 

 an acid reaction. The delicate network 

 within the nucleus consists apparently of 

 the nuclein, a substance which stains with 



carmine and other dyes, a property which 

 enables the changes, which take place in 

 the network in the production of young 

 cells, to be more readily seen and followed 

 out by the observer. 



The mode of origin of the nucleus and 

 the part which it plays in the production of 

 new cells have been the subject of much 

 discussion. Schleiden, whose observations, 

 published in 1838, were made on the cells 

 of plants, believed that within the cell a 

 nucleolus first appeared, and that around it 

 molecules aggregated to form the nucleus. 

 Schwann again, whose observations were 

 mostly made on the cells of animals, con- 

 sidered that an amorphous material existed 

 in organized bodies, which he called cyto- 

 blastema. It formed the contents of cells, 

 or it might be situated free or external to 

 them. He figuratively compared it to a 

 mother liquor in which crystals are formed. 

 Either in the cytoblastema within the cells 

 or in that situated external to them, the 

 aggregation of molecules around a nucleolus 

 to form a nucleus might occur, and, when 

 once the nucleus had been formed, in its 

 turn it would serve as a center of aggrega- 

 tion of additional molecules from which a 

 new cell would be produced. He regarded 

 therefore the formation of nuclei and cells 

 as possible in two ways : one within pre- 

 existing cells (endogenous cell-formation), 

 the other in a free blastema lying external 

 to cells (free cell-formation). In animals, 

 he says, the endogenous method is rare, 

 and the customary origin is in an external 

 blastema. Both Schleiden and Schwann 

 considered that after the cell was formed 

 the nucleus had no permanent influence on 

 the life of the cell, and usually disappeared. 



Under the teaching principally of Henle, 

 the famous Professor of Anatomy in Got- 

 tingen, the conception of the free formation 

 of nuclei and cells in a more or less fluid 

 blastema, by an aggregation of elementary 

 granules and molecules, obtained so much 



