THE CELL; THE COLLOIDAL CONDITION 13 



it protoplasm, and in 1846 Von Mohl applied the same name to 

 the material in plant cells. 



The Cell Theory. — Mirabel in 1808 showed that all plants are 

 made up of cells, and Lamarck in 1809 extended this idea to ani- 

 mals, but the credit for the idea that every living plant and ani- 

 mal, however different in appearance, is composed of cell units 

 is generally given to the botanist, Schleiden, and the zoologist, 

 Schwann (1839), because Mirabel and Lamarck both emphasized 

 the cell wall rather than the cell contents. As Schwann stated 

 it: "The elementary parts of all tissues are formed of cells in an 

 analogous, though very diversified manner, so that it may be 

 stated that there is one universal principle of development for 

 the elementary parts of organisms, however different they may 

 be, and that this principle is the formation of cells." 



Recent research, however, has shown that before these two 

 Germans published on the "cell theory," the French physician 

 and botanist, Dutrochet (1776-1847), had (1) established the an- 

 atomical individuality of cells, (2) described the universal cellu- 

 lar structure of living plant and animal tissues, and (3) stressed 

 the importance of the cell as the physiological unit of the orga- 

 nism. To him, therefore, goes the delayed gratitude of biologists 

 for the establishment of the cellular nature of organic structures. 



The Cell. — The plant cell is generally limited or bounded on 

 the outside by a cellulose wall which is formed by the activity of 

 the protoplasm within. On the inside of the wall, lining it anc[ 

 filling more or less of the entire space, depending upon the ag« 

 and nature of the cell, is the viscid, nearly transparent, living 

 protoplasm. In most cells is at least one nucleus, a round, more 

 refractive body, which was first recognized by Robert Brown in 

 1831 to be of paramount importance as the center of cellular ac- 

 tivities. 



In 1861 Max Schultze showed that the substance which Du jar- 

 din had described and others had named was the same in plants 

 and animals. He then formulated what has been called the "pro- 

 toplasm doctrine," which states that the important physiologi- 

 cal and morphological unit of all organized life is the nucleated 

 mass of protoplasm. 



Cell Parts and Inclusions. — The protoplasm surrounding the 

 nucleus is now called cytoplasm. It may contain various organized 

 bodies, among which are the plastids, the most important of which 



