INTRODUCTION. 19 



from the rest of nature, and therefore require a 

 distinct origin, it makes little difference whether 

 we looked upon that origin as a single originat- 

 ing point or as thousands of independent crea- 

 tions. But so soon as it appeared that the 

 present condition of the earth's crust was formed 

 by the action of forces still in existence, and so 

 soon as it appeared that the forces outside of 

 living forces, including astronomical, physical 

 and chemical forces, are all correlated with 

 each other as parts of the same store of energy, 

 then the problem of the origin of living things 

 assumed a new meaning. Living things became 

 then a part of nature, and demanded to be in- 

 cluded in the same general category. The reign 

 of law, which was claiming that all nature's 

 phenomena are the result of natural rather than 

 supernatural powers, demanded some explanation 

 of the origin of living things. Consequently, when 

 Darwin pointed out a possible way in which living 

 phenomena could thus be included in the realm of 

 natural law, science was ready and anxious to re- 

 ceive his explanation. 



CYTOLOGY. 



A third conception which contributed to the 

 formulation of modern biology was derived from 

 the facts discovered in connection with the organic 

 cell and protoplasm. The significance of these 

 facts we shall notice later, but here we may 

 simply state that these discoveries offered to 

 students simplicity in the place of complexity. 

 The doctrine of cells and protoplasm appeared 



