122 REMINISCENCES OF 



In 1839 Professor Schwann, of the University of 

 Louvain, brought out his renowned work, " Micro- 

 " scopical Researches into the Accordance in Struc- 

 " ture and Growth of Animals and Plants." A little 

 previously, Dr. Schleiden, the Professor of Botany 

 in the University of Jena, published a collection of 

 papers, in which the cells and cell development seen 

 in the vegetable world were industriously investi- 

 gated, and, at the same time, Mirbel and others were 

 occupied with similar researches. Thus the extreme 

 importance of the cell in the life-history of plants 

 and animals soon became known and universally 

 recognised. 



A cell is a minute atom of a semi-fluid substance 

 that may or may not be invested by a " cell wall," 

 which is in the first instance an extremely thin 

 membrane. The contents of the cell are of a com- 

 posite character, and with varying characteristics, 

 though in the young state chiefly composed of what 

 is designated protoplasm. This compound element 

 can, and frequently does, remain for a long time in 

 active vitality, without being invested by a cell wall. 

 The latter is an effect of the vital activity of the 

 protoplasm, not its cause, but in most cases it is the 

 usual effect of that life. 



We now know that all the tissues alike of the 

 animal and of the plant have been produced by the 

 action of these cells. This truth was only realised 

 by biologists very slowly. Consequently, when Dr. 

 Sharpey first called my attention to the question of 



