PROTOPLASM AND THE CELL 



51 



It is no discredit to this theory or these men that they and many 

 other biologists of the time had erroneous ideas concerning the 

 essential features of the cell. Although Brown had recently dis- 

 covered the nucleus, the cell wall was thought to be the essential 

 part, though now we know it is not a universal structure of all 

 cells since practically no animal cells have a cell wall. The notions 

 of the origin of cells and the functional significance were almost 

 wholly fantastic, yet the cell theory proved to be such a unifying 

 generalization and inspiring stimulus to investigation that it became 

 the turning point in the development of biological study. 



Fig. 18. — Theodor Schwann (1810-1881^), the German zoologist who, in 1838 and 

 1839, collaborated with Schleiden in formulating the cell theory. (From Garrison, 

 History of Medicine, published by \Y. B. Saunders Company.) 



The bare statement that living beings are composed of cells soon 

 became inadequate as studies of cells progressed. It was soon found 

 that some tissues are made up not only of cellular structures but 

 included also certain noncellular materials produced by the cells. 

 The matrix, so abundant between the cells of cartilage, was soon 

 found to be noncellular and to be produced by the cartilage cells 

 which became embedded in it. This matrix is not strictly living 

 matter since it is inactive and passive as far as life processes are 

 concerned. Connective tissue fibers fall in the same category. Since 

 living bodies are composed of such an abundance of this noncellular 



