PROTOPLASM AND CELL 43 



2. Conductivity refers to the fact that the impulses produced by 

 stimuli or irritations at one point in protoplasm are conducted to 

 other parts of not only a single cell but also to adjoining cells. 



3. Contractility, which is the power of contraction and relaxation 

 that is common to the substance of every cell. 



4. Metabolism, the process of continual exchange of food and fuel 

 materials being built into the protoplasm, while, at the same time, 

 materials there are being oxidized to liberate kinetic energy, such as 

 heat and movement, and produce waste by-products. 



5. Growth is recognized as any increase in volume. When the rate 

 of the building side of metabolism exceeds the oxidation rate in the 

 protoplasm, there is storage of materials in the mass of the protoplasm 

 and hence growth. All protoplasm has this capacity. 



6. Reproduction is the capacity for producing new individuals of 

 the same kind. All living organisms are capable of this by some 

 means. Simple cell division is the most primitive process of repro- 

 duction among animals. 



Consciousness, which refers to the awareness of one's own exist- 

 ence, is frequently given as a property of protoplasm. It is certain 

 that some protoplasm possesses consciousness, but evidence of this 

 quality is rather intangible. Spontaneity is also considered a prop- 

 erty of protoplasm by some. To be certain that the activity and 

 source of all reaction comes from within is likewise rather difficult 

 of definite proof, so this is simply mentioned here as another prop- 

 erty which is often listed. 



Physical Nature of Protoplasm 



Protoplasm is a semifluid material which is heavier than water 

 and somewhat more refractive to light. Its physical constitution 

 is similar to glue or gelatin, rather than to crystalloids, such as 

 sugar or ordinary table salt (sodium chloride). Instead of being 

 in the form of a true solution like salt in water, it consists of sus- 

 pensions of relatively large molecular aggregations varying roughly 

 between 0.0001 and 0.000001 millimeter in diameter. These par- 

 ticles keep up an expression of energy in that they move against 

 each other as though they were dancing in a limited space. This 

 activity can be seen only with a special optical arrangement known 

 as the ultramicroscope and the phenomenon is known as Broivnian 

 movement (characteristic of colloidal substances). Protoplasm dif- 



