60 THE CELL DOCTRINE. 



"cell contents," and "nucleus";'' the "nucleolus," 

 though usually met in fully developed older forms, 

 is not considered an essential constituent of the 

 cell. The object of the "nucleus," according to* 

 Yirchow, is entirely connected with the life of the 

 cell, that which maintains it as an element and 

 which insures its reproduction. While to the "cell 

 contents" over and above the nucleus, that is the 

 " residual cell contents," is due the function of the 

 cell, that to which is due the contractility of mus- 

 cle, the neurility and sensation of nerve, and the 

 secretory office of the gland cell.* 



To secure the universal application of the cell 

 doctrine, it becomes necessary to eliminate from the 

 vegetable cell, the external non-nitrogenous mem- 

 brane known as cellulose, and restrict it to the nitro- 

 genized portion comprised in the primordial utricle as 

 the proper cell wall, and in the protoplasmic contents 

 of the cavity as the proper cell contents, which con- 

 tain also the nucleus. " It is only when we adhere 

 to this view of the matter, when we separate from 

 the cell all that has been added to it as an after-de- 

 velopment, that we obtain a simple, homogeneous, 

 extremely monotonous structure, recurring with ex- 

 traordinary frequency in living organisms."f 



More recently, however, Virchow is reported as 

 not regarding the "cell wall" as an essential part of 

 the cell, as stated in Cellular Pathology; but that a 



* Virchow, Cellular Pathology as based upon Physiological and 

 Pathological Histology. Second Edition. Translated by Frank 

 Chance, M.B., &c. Am. Edition, Philadelphia: 1863, p. 37. 



f Op. cit., pp. 31, 34. 



