INTRODUCTION 19 



upon animals in our laboratories cannot for a moment 

 be compared with the thoughtless cruelty of hunters and, 

 in the writer's opinion, with the abuse of pets by children. 



Vivisection has been effectively defended on the ground 

 that it has been indispensable to medical progress. This 

 argument will not be extended here but the question 

 asked by a great surgeon W. W. Keen may be repeated 

 for the consideration of the reader: " Reckoned in rab- 

 bits, what is the value of your wife, your husband, or 

 your child?" 



The Mechanistic Conception. Experimenters of the 

 present time believe that the organisms with which they 

 have to do are mechanisms in the sense that none of the 

 recognized principles of physics and chemistry are vio- 

 lated in their working. This conception is held in place 

 of an earlier one, now spoken of as that of the Vitalists, 

 according to which living things were regarded as unique 

 in character and not bound by all the limitations of 

 strict mechanisms. Of course it is recognized that there 

 is an abundance of mystery about life and its manifesta- 

 tions, but all progress toward a better understanding of 

 plants and animals has thus far been based on the view 

 that they exemplify the same laws which are accepted 

 as applicable to things not living. While this is true it 

 is probably correct to say that the physiologist of to-day 

 has a more adequate realization of the complexity of his 

 problems than his predecessor had a generation ago. It 

 must be borne in mind that, except for certain passages 

 in the treatment of the brain, the point of view is objec- 

 tive, that is, the concern is with what happens in a mate- 

 rial body and not with what is felt while the various 

 actions are going on. 



Brief reference has been made to the principles of the 

 indestructibility of matter and the conservation of 

 energy. These were adopted by men of science as the 

 result of work in the fields of chemistry and physics. 

 But we have every reason to Relieve that they hold good 

 for living forms of every grade, human beings included. 



