14 THE LIVING WORLD. 



plest living thing and the most complex compound 

 not alive, the less will be the difficulty in believing 

 in the natural origin of life. If we could find a 

 substance that was simply living matter with no 

 definite characteristics of any specific nature, this 

 would be the starting-point. From a priori grounds 

 we might expect that simple living matter would 

 appear before any definitely formed species. This 

 fact is the basis of the interest connected with the 

 study and speculation concerning protoplasm, the 

 supposed common factor of living things. In the 

 simplest forms of life we get down almost to pure 

 and simple protoplasm, and by taking from these 

 forms all of the common factors, we may suppose 

 that we obtain the characters of simple protoplasm 

 itself, and thus presumably the first form of life. 



There is another series of facts which can hardly 

 be called evidence, but which does at the same time 

 have a great influence in our interpretations of the 

 past. The long-continued study of nature has led 

 to the formulation of the law of continuity. Ac- 

 cording to this law, the processes of nature have 

 been those of continual slow change, such that the 

 history of any minute is explained by the conditions 

 of the preceding minute. The law admits of no 

 great breaks in the history of the processes in nature, 

 but assumes that where such breaks seem to exist, 

 the break is only in our knowledge, and not in the 

 nature itself. It is impossible that the acceptance 

 of this law should fail to have great influence in the 

 interpretation of the life history, for by means of it 

 a constant development is necessarily substituted 



