PHYSICAL AND PHYSIOLOGICAL METHODS 5 



and staining reagents and other physical or 

 chemical apparatus we separate out or render 

 distinguishable the details of structure. But 

 these details are only details of form, size, 

 colour, physical or chemical characters, and 

 spatial relations to other parts. The facts we 

 ascertain are physical and chemical facts; 

 and the methods we use are physical and 

 chemical methods. 



If, on the other hand, we are making a 

 physiological investigation, the same is no 

 less true. If we are investigating secretion 

 we are measuring the mass or volume of the 

 substances secreted, or their chemical com 

 position, or perhaps their osmotic pressure, 

 or concentrations of ions in them. If we 

 are investigating muscular contraction we 

 are measuring the rate and extent of the 

 contraction, or the accompanying heat pro 

 duction or chemical or electromotive pheno 

 mena. The phenomenon which we observe 

 is always some physical or chemical change. 

 The methods we use are physical and chemi 

 cal methods, and the resulting facts are 

 consequently physical and chemical facts. 



From the very nature of its methods and 



