METHODS 135 



The equilibrium of the animal mechanism may therefore 

 be studied in three different scales, chemical, colloid, and 

 anatomical. Clearly, then, we shall meet with three kinds 

 of causes of activity ruptures of equilibrium to set the 

 mechanism going. There will be causes of the anatomical 

 order of magnitude, colloid causes and chemical causes. 



The anatomical causes are all bodies existing in the sur- 

 rounding world in our human scale ; stones, trees, hin- 

 drances to our locomotion, wind, rain, and so on. To these 

 causes we respond by anatomical movements, the adapta- 

 tion of which to the preservation of life is what we call the 

 instinct of self-preservation. These anatomical movements 

 are naturally accompanied by colloidal and chemical move- 

 ments, but it is in the anatomical scale that we recognize 

 their utility. They are the anatomical functions, or func- 

 tions of the mechanism as a whole. 



Causes of the colloid order of magnitude are those which 

 act directly on the colloid states of our protoplasms and 

 have no direct relation with our anatomical mechanism. 

 Such are sonorous vibrations, foods (savour), toxins, etc., 

 and perhaps also electric phenomena. 



In certain cases the activity resulting from such causes 

 is confined to the colloid field. This takes place, for 

 example, when a toxin or food substance is injected into the 

 interior medium of an animal. The phenomena which 

 follow the injection are colloidal and so is the useful result 

 (fabrication of an antitoxic serum). 



In other cases the activity due to a colloid cause influences 

 the mechanism as a whole and determines anatomical move- 

 ments. The savour of a food moves us to swallow it or to 

 spit it out ; a discordant note makes us gnash our teeth or 

 even take to flight. 



Causes of the chemical order of magnitude are those able 



