12 LIVING AND LIFELESS MATTER 



To continue the analogy a bit further. New fuel is needed 

 to maintain a fire, so new food is needed to prevent death 

 through continued waste and to provide energy for continued 

 activity. The new coal must first undergo a certain amount of 

 preparation before it undergoes oxidation; it must be broken 

 into small pieces, and must be raised to a certain temperature 

 before active combustion takes place. Similarly, food con- 

 sisting usually of lifeless proteins, carbohydrates and fats 

 derived from other animals or plants, must be disintegrated 

 and prepared for assimilation, and this finely divided food 

 material is then distributed to all parts of the organism. The 

 process of thus preparing the food is called digestion, and is 

 mainly a process of hydrolysis of food materials. In biology 

 the two processes of waste and repair are usually considered 

 together under the term Metabolism, destructive metabolism 

 called katabolism being the sum of processes concerned with 

 the breaking down or combustion of protoplasmic substances, 

 and constructive metabolism, called anabolism, being the sum 

 of processes having to do with repair and growth. Just how the 

 finely divided food particles are added to the protoplasmic 

 molecules is unknown, but it is certain that the addition takes 

 place uniformly and in all parts of the organism, and that by 

 such uniform additions of new materials growth of the organism 

 takes place. From its mode of addition we have the third 

 property of living matter: 



3. GROWTH BY INTUSSUSCEPTION 



This is distinguished from growth by accretion as seen in the 

 enlargement of a crystal, for example, where new particles are 

 added to the outside of the existing structure. Obviously such 

 growth or increase in amount of protoplasm together with its 

 differentiation, can take place only when the waste or combus- 

 tion of protoplasmic substances is less than the new materials 

 added. When the constructive processes exceed the destruc- 

 tive, more material is added to the protoplasm than is lost 

 by waste, and growth results. This growth continues until a 



