Dana — American Journal of Science, 1818-1918. 7 



Although not falling* within our sphere, it would be 

 wrong, too, not to recognize also the growth of medicine, 

 especially through the knowledge of bacteria and their 

 functions, and of disease germs and the methods of com- 

 bating them. The world can never forget the debt it 

 owes to Pasteur and Lister and many later investigators 

 in this field. 



To follow out this subject further would be to encroach 

 upon the field of the chapters following, but, more 

 important and fundamental still than all the facts dis- 

 covered and the phenomena investigated has been the 

 establishment of certain broad scientific principles which 

 have revolutionized modern thought and shown the rela- 

 tion between sciences seemingly independent. The law 

 of conservation of energy in the physical world and the 

 principle of material and organic evolution may well be 

 said to be the greatest generalizations of the human 

 mind. Although suggestions in regard to them, particu- 

 larly the latter, are to be found in the writings of early 

 authors, the establishment and general acceptance of 

 these principles belong properly to the middle of the 

 nineteenth century. They stand as the crowning achieve- 

 ment of the scientific thought of the period in which we 

 are interested. 



Any mere enumeration of the vast fund of knowledge 

 accumulated by the efforts of man through observation 

 and experiment in the period in which we are interested 

 would be a dry summary, and yet would give some meas- 

 ure of what this marvelous period has accomplished. As 

 in geography, man's energy has in recent years removed 

 the reproach of a "Dark Continent," of " unexplored " 

 central Asia and the once "inaccessible polar regions,' ' 

 so in the different departments of science, he has opened 

 up many unknown fields and accumulated vast stores of 

 knowledge. It might even seem as if the limit of the 

 unknown were being approached. There remains, how- 

 ever, this difference in the analogy, that in science the 

 fundamental relations — as, for example, the nature of 

 gravitation, of matter, of energy, of electricity; the 

 actual nature and source of life — the solution of these 

 and other similar problems still lies in the future. What 

 the result of continued research may be no one can pre- 

 dict, but even with these possibilities before us, it is 

 hardly rash to say that so great a combined progress of 



