CELL-FORMATION. 133 



CON TENTS /or the purpose of normal cell-formation is con- 

 sequently this ; that a nucleus is formed, and that this 

 nucleus individualizes a portion of the contents by attrac- 

 tion. The portions may be indeterminate or determinate. 

 If the former, the quantity of contents isolated around 

 the nucleus is uncertain. If the latter, either the whole 

 contents or a definite fraction (J, i, i, , |, i) becomes indi- 

 vidualized around the nucleus, the denominator of the 

 fraction giving the number of simultaneously individu- 

 alized portions of contents. 



CELL-FORMATION is the individualization of a portion 

 of contents, immediately followed by the formation of 

 membrane. The definition of cell-formation depends on the 

 combination of the two constituent definitions. Normal 

 cell-formation, therefore, in so far as it is endogenous, 

 consists in this: 



A nucleus is formed in the contents of the parent-cell ; 

 this individualizes a portion of the contents by attraction, 

 and this individualized portion becomes coated with a 

 membrane by secretion over the whole of its surface. 



e/ t/ c/ 



But since, in animals, cell-formation also occurs outside 

 cells, likewise commencing with a nucleus, and since in 

 the generatio spontanea the first cells of plants or animals 

 are formed either in external media or in other cells, in 

 such a manner that these certainly cannot be regarded as 

 parent-cells in the proper sense of this word, the definition 

 of normal cell-formation must be brought into a more 

 general expression. 



In organic substances (which in animal cell-formation 

 must contain proteine-compounds, in vegetable, azotized 

 and unazotized compounds, such as albumen, gum and 

 sugar) a nucleus originates which, by attraction, indivi- 

 dualizes a portion of the organic substances surrounding it; 

 the individualized portion of organic substances becomes 

 clothed by a membrane through secretion over its whole 

 surface. 



In vegetable cell-formation the substance secreted as 

 membrane is composed of ternary unazotized substances. 



