88 THE CELL DOCTRINE. 



The size of the elementary part, as thus composed, 

 is extremely various. The smallest' particles of ger- 

 minal matter, measured by Dr. Beale, are less than 

 j-^jI-^-^-^ of an inch in diameter, and would not be 

 called cells in the ordinary sense of the word, yet 

 they are functionally such ; that is,. they grow, multi- 

 ply by division, and under appropriate circumstances 

 assume the characters of fully formed cells. On the 

 other hand, the largest epithelial cells, including 

 their germinal matter and formed material, are often 

 as large as the ^ Jjj of an inch in diameter, or larger ; 

 cells of morbid growths are sometimes ^J,,, while the 

 hunian ovum, which is a typical cell, varies from the 

 s^-g- to Tin of an inch. .Pure germinal matter is 

 rarely seen in masses as large as the jj^ of an inch 

 in diameter, without breaking up into smaller par- 

 ticles of germinal matter, and as constituting the 

 nuclei of fully formed cells, is usually from g^'^j- to 

 ^^0 5 of an inch in diameter. 



The method of ■production of formed material is best 

 studied in the epithelial structures, particularly in 

 the epithelium lining mucous cavities, of which sec- 

 tions may be easily made down to the vessels whence 

 their nourishment is obtained. In the deep layers, 

 next the nutrient surface, the cells will be found to 

 consist of almost pure germinal matter (frontispiece, 

 Fig. 1), imbedded in a soft, mucus-like, yet continuous 

 formed matter. These masses of germinal matter 

 divide and subdivide, pushing the older masses to- 

 wards the surface, to make up for those which are 

 constantly exfoliated. While this is going on, how- 

 ever, the germinal matter keeps increasing in size 



