VI PREFACE. 



There is therefore a philosophy of the science which 

 deals with the phenomena of life and death — i.e., of 

 physiology. I have endeavoured to give a summary 

 of this philosophy in this volume. I have had in 

 view two classes of readers. In the first place there 

 are readers of general culture who are desirous of 

 knowing something of the trend of ideas in biology. 

 They already form quite a large section of the great 

 public. 



These scholars and inquirers, with Bacon, believe 

 that the only science is general science. What they 

 want to know is not what instruments we use, our 

 processes, our technique, and the thousand and one 

 details of the experiments on which we spend our 

 lives in the laboratory. What they are interested in 

 are the general truths we have acquired, the pro- 

 blems we are trying to solve, the principles of 

 our methods, the progress of our science in the 

 past, its state in the present, its probable course in 

 the future. 



But I venture to think that this book is also 

 addressed to another class of readers, to those whose 

 professional study is physiology. To them it is 

 dedicated. They have been initiated into the 

 mysteries of the science. They are learning it by 

 practice. That is the right method. Practice makes 

 perfect. Claude Bernard used to say that in order 

 to be an expert in experimental science you must 

 first be " a laboratory rat." And among us there are 

 many such "laboratory rats." They are guided in 



