72 Presidential Address 



thority in denials. To deny effectively 

 needs much more comprehensive know- 

 ledge than to assert. And abstraction is 

 essentially not comprehensive: one can- 

 not have it both ways. Science employs 

 the methods of abstraction and thereby 

 makes its discoveries. 



The reason why some physiologists 

 insist so strenuously on the validity and 

 self-sufficiency of the laws of physics and 

 chemistry, and resist the temptation to 

 appeal to unknown causes even though 

 the guiding influence and spontaneity of 

 living things are occasionally conspicuous 

 as well as inexplicable is that they are 

 keen to do their proper work; and their 

 proper work is to pursue the laws of 

 ordinary physical Energy into the intri- 

 cacies of "colloidal electrolytic structures 

 of great chemical complexity" and to 

 study its behaviour there. 



What we have clearly to grasp, on their 

 testimony, is that for all the terrestrial 

 manifestations of life. the ordinary phys- 

 ical and chemical processes have to serve. 

 There are not new laws for living matter, 



