METABOLISM 77 



life not only goes on upon the earth but in the earth 

 as well, and that the soil, far from being the lifeless 

 mass of rocks and dirt we are accustomed to con- 

 sider it, is pulsing with life in every granule, harbor- 

 ing a multitude of different organisms that live in 

 darkness and for the most part without oxygen, 

 but whose activities are so vital for the more familiar 

 life above the ground that one could not exist without 

 the other. 



Nature of the Energy Transformed. -- M ove- 

 ment. - - The latent energy of chemical affinity 

 may be transformed into all the other forms of 

 energy known. The movements of an animal are 

 primarily brought about by the contractility of its 

 protoplasm, which is almost always differentiated 

 (except in Protozoa) as muscular tissue. 



Intracellular circulation has been previously men- 

 tioned. This is a form of motion probably univer- 

 sal in animals and plants. The simplest form of 

 motion, after this, is that described in the previous 

 chapter in connection with the movements of 

 leucocytes, and known as amoeboid, because it is 

 the characteristic and only form of locomotion 

 possessed by Amoeba. A similar mode of unlocalized 

 movement is also found in many pigment cells and 

 in the primitive connective tissue cells of the develop- 

 ing embryo. 



The majority of the Protozoa move by means of 

 special organs of locomotion, differentiated either 

 as cilia, covering all or parts of the cell-body, or as 



