36 THE STEUCTUBAL UNITS OP LIVING MATTER 



in the cytoplasm and continually decreases in size until it 

 finally disappears entirely. What has happened? Simply 

 this: This curious liquid has selected a food substance, 

 broken it up, dissolved it, and distributed the dissolved 

 product all over the body; while the fact that the product 

 is no longer visible shows that it must have been trans- 

 formed into protoplasm itself. In other words, proto- 

 plasm is capable of distinguishing and taking in food, of 

 dissolving or digesting it, and of making new protoplasm 

 out of it. 



Finally, we may note that one of the vacuoles is larger 

 than the others and expands and contracts rhythmically. 

 As it expands this vacuole fills with a liquid that seeps 

 from the protoplasm, and which the contracting vacuole 

 forces out into the surrounding water. This liquid is 

 the waste matter produced by the active protoplasm, and 

 is formed by the breaking up of the chemical composi- 

 tion of the old protoplasm. Protoplasm, therefore, not 

 only can assimilate food, that is, build it up into new 

 protoplasm, but also has the power to dispose of its waste 

 products. 



Other experiments have taught that the amoeba absorbs 

 oxygen as well as food, and that in the breaking up of the 

 protoplasm the carbon which it contains unites with this 

 oxygen and produces carbon dioxide with a consequent 

 production of heat and power. The carbon dioxide is 

 given off as a waste from the surface of the c3i;oplasm. 



We may summarize then, as follows, the properties of 

 this peculiar fluid, protoplasm, as exhibited in the amceba: 



(a) Power of automatic movement. 



(b) Sensitiveness to stimuli. 



(c) Power to select food and to take it in. 



