THE LIVING WORLD 197 



a particle of protoplasm. Therefore every other kind of 

 substance which may be found in every kind of plant or 

 animal, must have been formed through it, and be, in 

 fact, a secretion from protoplasm. Such is the rosy 

 cheek of an apple, or of a maiden, the luscious juice of 

 the peach, the produce of the castor-oil plant, the baleen 

 that lines the whale's enormous jaws, as well as that 

 softest product, the fur of the chinchilla. Indeed every 

 particle of protaplasm requires, in order that it may live, 

 a continuous process of exchange. It needs to be con- 

 tinuously first built up by food, and then broken down 

 by discharging what is no longer needful for its healthy 

 existence. Thus the life of every organism is a life of 

 almost incessant change, not only in its being as a whole, 

 bat in that of all its protoplasmic particles also. 



Prominent among such processes is that of an inter- 

 change of gases between the living being and its environ- 

 ment. This process consists in an absorption of oxygen 

 and a giving- out of carbonic acid, which exchange is 

 termed respiration. 



Lastly, protoplasm has a power of motion when 

 appropriately acted on. It will then contract or expand 

 its shape by alternate protrusions and retractions of 

 parts of its substance. These movements are termed 

 amoebiform, because they quite resemble the movements 

 of a small animalcule which is named amoeba (Fig. 29). 



Such is the ultimate structure, and such are the 

 fundamental activities (or functions) of living organisms 

 (so far as they can here be described), from the lowest 

 animalcule and unicellular plant, up to the most complex 

 organisms and the body of man himself. 



It. has been explained how it is that organisms of 

 complex structure become such by means of a spon- 

 taneous division and multiplication of their component 



