THE CELL DOCTRINE. 89 



until the cells arrive half way towards the surface, 

 by absorption of nutrient pabulum, which has to dif- 

 fuse itself through any formed material already ex- 

 isting. At the sarrie time, a portion of the germinal 

 mattei' is being converted into formed material, 

 which accumulates on its surface, within that already 

 formed, stretching it, and becoming more or less in- 

 corporated with it. Thus, both constituents of the cell 

 increase up to a certain point, the cells constantly growing 

 in consequence. As new cells are, however, produced 

 from below," the older ones are removed farther and 

 farther away, the formed matter becoming more and 

 more impervious to nutrient pabulum. At length a 

 point is attained when the entire cell ceases to in- 

 crease in size, since no pabulum reaches the masses 

 of germinal matter, though the latter is still being 

 converted into formed material. Hence, the masses 

 of germinal matter actually grow smaller as the cell 

 increases in age ; and when the periphery is reached, 

 there remains but a small nucleus of germinal matter, 

 with a large quantity of formed material. Thus, we 

 are enabled to judge of the age of the cell by the 

 relative quantity of germinal matter and formed 

 material ; if the former be large, and the latter small, 

 the cell is young, whereas, if the opposite relation 

 exists, the cell is old and almost ready to exfoliate. 

 But exfoliation in health probably does not take 

 place until the last particle of germinal matter dies, 

 and the entire cell becomes a mass of passive, life- 

 less, formed material. 



The production of formed material from germinal 

 matter may also be studied in the conversion of the 



