THE CELL DOCTRINE. 149 



from the ^i^ to yj-j- of an inch (.105 mm. to .21 

 mm.). The smallest particles of germinal matter 

 above alluded to would not be called cells in the or- 

 dinary sense of the word, but they are such consist- 

 ently with ou(r definition, and it must moreover be 

 remembered that the term is only applied to such 

 particles of matter endowed with the life properties 

 of reproduction, nutrition, growth, and development. 

 No particle of oil, inorganic or other matter, which 

 does not possess these properties can be characterized 

 as a living cell, whatever its size. 



Pure germinal matter is rarely seen in masses as 

 large as the 5 J^ of au inch (.05 mm.), since it usually 

 breaks up into smaller masses to form independent 

 cells before it reaches this size. As constituting the 

 nuclei of fully formed cells, it is usually from the 

 bttW to s^'j-jT °^ ^^ inch (004. mm. to 008. ram.) in 

 diameter. While nuclei exhibit less variation in size 

 than do the cells, they are also more constant in shape, 

 being generally round or oval. Sometimes, however, 

 they also exhibit a stellate shape. 



The Origin of Cells. — It is to be regretted that this 

 most important question as to the exact origin of 

 cells is not yet definitely settled. A very short time 

 ago the proposition omnis cellula e celluld wa,% thought 

 to have been abundantly proven, and that all living 

 things come from previously existing things, was 

 generally admitted. But although this view has been, 

 in the conception of some, shaken by more recent ex- 

 periment, it still remains the only law of cell forma- 

 tion in the minds of most physiologists, and I be- 

 lieve there are none who deny that it forms in all 



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