THE CELL A UNIT OF LIFE. 1 23 



has been regarded during the last thirty-five years as the 

 true basis of all morphological and physiological know- 

 ledge in Zoology and Botany, it is especially necessary t ) 

 conceive the cell as an integral organism, or, in other words, 

 an independent living being. When by dissection we have 

 separated the developed body of a Man, or of any other 

 animal or plant, into its organs, and when we then proceed 

 further to examine by means of the microscope the more 

 minute constituents of these larger organs, which give the 

 form to the whole organism, we are surprised to find that all 

 these various parts are made up of the same fundamental 

 constituents or structural elements ; and these are cells. 

 Whether we examine anatomically and by means of the 

 microscope, a leaf, a flower, or a fruit ; or again, a bone, a 

 muscle, a gland, or a piece of skin, etc., we everywhere find 

 one and the same form-element, which has been called the 

 Cell, since Schleiden gave it that name. Very different 

 views are held as to the real nature of this cell ; but what- 

 ever we think of it, it must be regarded as an independent 

 life-unit. The tiny cell is, as Brlicke sa.ys, " an elementary 

 organism," or, as Virchow expresses it, a " seat of life " 

 (Lehensheerd). It is, perhaps, most accurately described as 

 the organic unit of form of the lowest grade, as an indi- 

 vidual of the first order (Generelle Morpliologie, vol. i. 

 p. 269). This unit is such both in anatomical form, and in 

 physiological function. In the Protista, in the one-celled 

 plants and primitive animals, the whole organism per- 

 manentl}' consists only of a single cell. On the contrary, in 

 most animals and plants, it is only in the earliest period 

 of individual existence that the organism is a simple cell ; 

 it afterwards forms a cell-society, or, more correctly, an 



