82 BIOLOGY AND PHYSICAL SCIENCES 



preliminary objection. Whatever the nature 

 of the actually living parts of an organism 

 may be, all that we can do in investigating 

 them, it may be pointed out, is to observe 

 and measure the physical and chemical 

 changes resulting from their activity. We 

 can measure the shortening of a muscle, 

 the pull it produces, the oxygen it absorbs, 

 the electrical changes which accompany 

 its excitation. All these are physical and 

 chemical changes, however ; and the whole 

 of physiology consists, and can only consist, 

 of such observations and measurements, It 

 must, therefore, from the very nature of its 

 data, be a physical and chemical science in so 

 far as it is a science at all. 



The reply to this is that apparent physi 

 cal and chemical changes are the signs or 

 sensuous data which point to the underlying 

 living activity. Just as the physicist has no 

 direct detailed knowledge of matter, but in 

 fers its properties and measures its amount 

 from various sensuous data, so the physi 

 ologist infers the nature and activities of a 

 living organism from sensuous data. But to 

 the physiologist the outward appearances of 



