UNSOLVED PROBLEMS OF SCIENCE. 41 



sional names of negative and positive, we know about as mucli 

 now as Franklin knew a century and a half ago. 



I have selected the elementary atoms and the ether as two 

 instances of the obscurity that still hangs over problems which 

 the highest scientific intellects have been investigating for sev- 

 eral generations. A more striking but more obvious instance still 

 is life animal and vegetable life the action of an unknown 

 force on ordinary matter. What is the mysterious impulse which 

 is able to strike across the ordinary laws of matter, and twist 

 them for a moment from their path? Some people demur to the 

 use of the term " vital force " to designate this impulse. In their 

 view the existence of such a force is negatived by the fact that 

 chemists have been able by cunning substitutions to produce arti- 

 ficially the peculiar compounds which in Nature are only found 

 in organisms that are or have been living. These compounds are 

 produced by some living organism in the performance of the 

 ordered series of functions proper to its brief career. To counter- 

 feit them as has been done in numerous cases does not enable 

 us to do what the vital force alone can effect to bring the organ- 

 ism itself into existence, and to cause it to run its appointed 

 course of change. This is the unknown force which continues to 

 defy not only our imitation but our scrutiny. Biology has been 

 exceptionally active and successful during the last half century. 

 Its triumphs have been brilliant, and they have been rich enough 

 not only in immediate result but in the promise of future ad- 

 vance. Yet they give at present no hope of penetrating the great 

 central mystery. The progress which has been made in the study 

 of microscopic life has been very striking, whether or not the 

 results which are at present inferred from it can be taken as con- 

 clusive. Infinitesimal bodies found upon the roots of plants have 

 the proud office of capturing and taming for us the free nitrogen 

 of the air, which, if we are to live at all, we must consume and 

 assimilate, and yet which, without the help of our microscopic 

 ally, we could not draw for any useful purpose from the ocean of 

 nitrogen in which we live. Microscopic bodies are convicted of 

 causing many of the worst diseases to which flesh is heir, and the 

 guilt of many more will probably be brought home to them in 

 due time ; and ther exercise a scarcely less sinister or less potent 

 influence on our race by the plagues with which they destroy 

 some of the most valuable fruits of husbandry, such as the potato, 

 the mulberry, and the vine. Almost all their power resides in 

 the capacity of propagating their kind with infinite rapidity, and 

 up to this time science has been more skillful in describing then- 

 ravages than in devising means to hinder them. It would be un- 

 grateful not to mention two brilliant exceptions to this criticism. 

 The antiseptic surgery which we owe chiefly to Lister, and the 



