INTRODUCTION. 15 



is evident that the aim of biological study must 

 be to test these conceptions and carry them out 

 into details. The chemical and mechanical laws 

 of nature must be applied to vital phenomena in 

 order to see whether they can furnish a satisfac- 

 tory explanation of life. Are the laws and forces 

 of chemistry sufficient to explain digestion ? Are 

 the laws of electricity applicable to an under- 

 standing of nervous phenomena ? Are physical 

 and chemical forces together sufficient to explain 

 life ? Can the animal body be properly regarded 

 as a machine controlled by mechanical laws ? Or, 

 on the other hand, are there some phases of life 

 which the forces of chemistry and physics cannot 

 account for ? Are there limits to the application 

 of natural law to explain .life ? Can there be 

 found something connected with living beings 

 which is force but not correlated with the ordinary 

 forms of energy ? Is there such a thing as vital 

 energy, or is the so-called vital force simply a 

 name which we have given to the peculiar mani- 

 festations of ordinary energy as shown in the 

 substance protoplasm ? These are some of the 

 questions that modern biology is trying to an- 

 swer, and it is the existence of such questions 

 which has made modern biology a new science. 

 Such questions not only did not, but could not, 

 have arisen before the doctrines of the conserva- 

 tion of energy and evolution had made their im- 

 pression upon the thought of the world. 



Significance of the New Biological Problems. It 

 is further evident that the answers to these ques- 

 tions will have a significance reaching beyond 

 the domain of biology proper and affecting the 

 fundamental philosophy of nature. The answer 

 will determine whether or not we can accept in 



