10 KEPORT— 1900. 



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, considered 

 that an amorphous material existed in organised bodies, which he called 

 oytoblastema. 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 centre of aggregation 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 customaiy 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 Pi'ofessor of 

 Anatomy in Gottingen, 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 credence, especially amongst 

 those who were engaged in the study of pathological processes, that the 

 origin of cells within pre-existing cells was to a large extent lost sight of. 

 That a parent cell was requisite for the production of new cells seemed to 

 many investigators to be no longer needed. Without doubt this con- 

 ception of free cell-formation contributed in no small degree to the 

 belief, entertained by various observers, that the simplest plants and 

 animals might arise, without pre-existing parents, in organic fluids desti- 

 tute of life, by a process of spontaneous generation ; a belief which pre- 

 vailed in many minds almost to the present day. If, as has been stated, 

 the doctrine of abiogenesis cannot be experimentally refuted, on the other 

 hand it has not been experimentally proved. The burden of proof lies 

 with those who hold the doctrine, and the evidence that we possess is all 

 the other way. 



MultiiJlication of Cells. 



Although von Mold, the botanist, seems to have been the first to 

 recognise (1835) in plants a multiplication of cells by division, it was not 

 until attention was given to the study of the egg in various animals, and 

 to the changes which take place in it, attendant on fertilisation, that in 

 the course of time a much more correct conception of the origin of the 

 nucleus and of the part which it plays in the forpiation of new cells was 

 obtained. Before Schwann had published his classical memoir in 1839, 



