6 THE BOOK OF NATURE STUDY 



process of building up and breaking down, of construction and 

 destruction, and that ferments play a very important part. [If 

 there is sufficient knowledge of chemistry, arrange a series of 

 carbon compounds, from relatively simple ones to the height 

 of complexity in proteids. Thus the formula of egg albumin 

 is often stated as C 204 H322N 5 2O 66 S 2 . Compare the body with a 

 manufactory, noting the raw materials, their early transforma- 

 tions, the finished products, and the waste products. But we 

 have very little knowledge as yet of the " secret room " in the 

 manufactory where the gist of the business is hidden.] 



Summary. Although no one is wise enough to tell completely 

 what is meant by the simple word alive, it is safe to say that 

 active life involves the following facts (a) The living organism 

 has the power of growth at the expense of material different 

 from itself. () The living organism has usually the power of 

 reproducing other organisms like itself, (c) The living organism 

 is subject to ceaseless chemical change, in which the complex 

 substances known as proteids are essentially involved, and yet 

 it has the power of persistence, of remaining more or less the 

 same for prolonged periods, (d) The living organism gives effective 

 responses to external stimuli ; it has a power of control and self- 

 regulation, it has a unified behaviour. 



SECTION 2. THE EVERYDAY ACTIVITIES OF ANIMALS. There 

 is a contrast between everyday activities, which are always 

 going on, and the periodic activities of growing and reproducing. 



The everyday activities or functions of the animal body are 

 five. There are the two " master-activities " of contractility 

 and of irritability, of the muscular and of the nervous systems 

 respectively, of moving and feeling in the wide sense. These make 

 life worth living. On a different plane are the three " auxiliary " 

 or " sustentative functions " which keep the two master-activities 

 agoing. These are nutrition, including the ingestion, digestion, 

 and final incorporation or absorption of food ; respiration, in- 

 cluding the absorption of oxygen (really a gaseous food) to keep 

 the vital combustion agoing, and the elimination of carbon 

 dioxide (really a gaseous waste) ; and excretion, the filtering out 

 of the nitrogenous waste, part of the ashes of the living fire. 



