CHAPTER I 



GENERAL SKETCH OF THE CELL 



" Wir haben gesehen, dass alle Organismen aus wesentlich gleichen Theilen, namlich aus 

 Zellen zusammengesetzt sind, dass diese Zellen nach wesentlich denselben Gesetzen sich 

 bilden und wachsen, dass also diese Prozesse iiberall auch durch dieselben Krafte hervorge- 

 bracht werden miissen." Schwann. i 



In the passage quoted above Schwann expressed a truth which 

 subsequent research has established on an ever widening basis ; and 

 we have now more than ever reason to believe that despite unending 

 diversity of form and function all cells may be brought into definite 

 relation to a common morphological and physiological type. We are, 

 it is true, still unable to specify all its essential features, and hence 

 can give no adequate brief definition of the cell. For practical pur- 

 poses, however, no such definition is needed, and we may be content 

 with the simple type that has been familiar to histologists since the 

 time of Leydig and Max Schultze. 



It should from the outset be clearly recognized that the term 

 "cell" is a biological misnomer; for cells only rarely assume the 

 form implied by the word of hollow chambers surrounded by solid 

 walls. The term is merely an historical survival of a word casually 

 employed by the botanists of the seventeenth century to designate 

 • the cells of certain plant-tissues which, when viewed in section, give 

 somewhat the appearance of a honeycomb.- The cells of these tis- 

 sues are, in fact, separated by conspicuous solid w^alls which were 

 mistaken by Schleiden, followed by Schwann, for their essential -part. 

 The living substance contained within the walls, to which Hugo von 

 Mohl gave the Xizxw^ protoplasm'^ (1846), was at first overlooked or 

 was regarded as a waste-product, a view based upon the fact that in 

 many important plant-tissues such as cork or w^ood it may wholly 

 disappear, leaving only the lifeless walls. The researches of Berg- 

 mann, Kolliker, Bischoff, Cohn, Max Schultze, and many others 



^ Untersiuhiingen, p. 227, 1839. 



-The word seems to have been first employed by Robert Hooke, in 1665, to designate 

 the minute cavities observed in cork, a tissue which he described as made up of "little 

 boxes or cells distinct from one another " and separated by solid walls. 



^ The same word had been used by Purkinje some years before (1840) to designate the 

 formative material of young animal embryos. 



c 17 



