OUTSTANDING BIOLOGICAL ADVANCES n 



Brown (1831), the work of Johannes Mliller in animal 

 physiology, the development of vegetable morphol- 

 ogy by Hofmeister and of vegetable physiology by 

 Sachs and Pfeffer. These are biological, but im- 

 portant as they were, they did not influence the whole 

 field of biological science as did those events now 

 referred to as the outstanding biological advances of 

 the century. 



To avoid repeated explanation, it is to be under- 

 stood that the term "biological" is generic and im- 

 plies botanical as well as zoological advances, but it is 

 used here in the restricted sense of "biological" 

 from the animal side. 



Considered from the standpoint of wide influence, 

 there are five biological advances of the nineteenth 

 century to which all others are subordinate. These 

 are: the discovery of protoplasm; the formulation of 

 the cell- theory; the establishment of the theory of 

 organic evolution; the demonstration of the germ- 

 theory of disease in connection with the rise of 

 bacteriology, and, fifth, the experimental study of 

 heredity. There was a parallel development of 

 these subjects but, for clearness, separate considera- 

 tion is necessary. 



The Discovery of Protoplasm. The scientific 



