CHAPTER VII 



THE CELL THEORY 



"The cell theory furnishes the starting point for all modem 

 studies in biology and enables all students to speak the same 

 language," says a twentieth century writer. The recognition of the 

 fact that animals and plants are constructed on a similar plan must 

 be placed among the most important discoveries of the nineteenth 

 century prolific as that century has been in scientific achievement. 

 "No other biological generalization," says Professor Wilson, 

 referring to the cell theory, "save only the theory of or- 

 ganic evolution has brought so many diverse phenomena 

 under a common point of view, or has accomplished more for the 

 unification of knowledge." By the term "cell-theory" is understood 

 the teaching that all animal and plant tissues are composed of units 

 known as "cells," which term as we shall see is inappropriate so far as 

 the actual things designated by it are concerned. The cell-theory is 

 a generalization which places animals and plants on a basis of similar- 

 ity of structure. 



Anticipated in the Seventeenth Century: The cell doctrine was 

 anticipated as far back as the seventeenth century, for it is to a 

 worker of the mid-seventeenth century that we are endebted for the 

 term "cell." Robert Hooke, an English microscopist, experimented 

 with cork, which he declared to be made up of "little boxes or *cells* 

 distinguished from one another." He made thin sections by means 

 of a pen knife and found them to be all "cellular or porous in the man- 

 ner of a honeycomb." Malpighi and Leeuwenhoek, in the seventeenth 

 century, made drawings which have been preserved showing the cell 

 structure of plants; we may therefore conclude that the cell theory 

 announced in 1838, was foreshadowed by seventeenth century work- 

 ers. Wolff, an acute scientific observer in 1759 worked out the 

 identity of plants and animals, as shown by their development. Hux- 

 ley summarizes Wolff's view of the development of elementary parts 

 as follows: "Every organ, according to him, is composed at first of 

 a little mass of clear viscous nutritive fluid which possesses no or- 

 ganization of any kind, but is at most composed of globules. In this 

 semi-fluid mass cavities are now developed; these if they remain 

 round or polygonal, become the subsequent cells; if they elongate, 

 the vessels; and the process is identically the same whether it is ex- 

 amined in the vegetating point of a plant or the young budding organs 

 of an animal." 



Bichat's Contribution: Though his connection with th^e cell 

 theory is open to question, the name of Bichat is deserving of mention 

 in discussing it. Marie Francois Xavier Bichat, bom in France in 

 1771, is noted as the founder of histology. He studied in Paris under 

 the great surgeon Desault. He was himself made professor of anatomy 

 at the age of twenty-six years, a position which he held until death 

 relieved him of his labors at the early age of thirty-one. It is related 



