THE DEEPENING OF PHYSIOLOGY. 311 



will be of special interest to determine whether in 

 those animals which are active as soon as they are 

 born, and which can at once assume the characteristic 

 attitude of the species, the fibres of the cerebrum 

 are completely developed at the time of birth." * 



THE LIFE OF CELLS. 



The Cell-Doctrine. — A recognition of the impor- 

 tance of cells as structural and functional units was 

 one of the distinctive biological steps of the nine- 

 teenth eentury. 



'* Without hesitation I should say that one of the 

 greatest achievements of biology in the nineteenth cen- 

 tury was the recognition that plants and animals are 

 composed of cells, or, more generally expressed, of 

 numberless very minute, elementary organisms. By 

 the co-operation of famous biologists — I mention only 

 Purkinje, Schleiden and Schwann, Hugo von Mohl, 

 Nageli, Kemak, Kolliker and Virchow, Briicke, Cohn 

 and Max Schultze — our knowledge of the organisation 

 of living substance has been greatly extended and deep- 

 ened. In the theory of cells and protoplasm, anatomy 

 and physiology secured a firm foundation similar to the 

 theory of atoms and molecules in chemistry." * 



Speaking of the cell-theory, Prof. E. B. Wilson 

 gives a similar verdict, " No other biological general- 

 isation, save only the theory of organic evolution, has 

 brought so many apparently diverse phenomena un- 

 der a common point of view, or has accomplished 

 more for the unification of knowledge." % 



The cell-doctrine includes three propositions: — 

 (1) Morphological, that all living creatures have a 



*Sir William Turner, loe. cit., p. 785. 



fProf. O. Hertwig, Die Entwicklung der Biologie im 19 

 Jahrhundert : Jena, 1900, p. 5. 



t The Cell in Development and in Inheritance, 2nd ed., 

 1900. 



