8 PHYSIOLOGY OF MUSCLES AND NERVES. 



like Amoehcc, and like the latter they even absorb matter, 

 such as granules of any colouring substance which may 

 have been added, from the blood-fluid — they eat, that 

 is — and after a time they again reject this matter. 

 Moreover, the other form of motion described above, 

 the protoplasmic movements or granule currents, may 

 also be seen in parts of compound organisms. If the 

 tiny hairs of the stinging nettle are placed under the 

 microscope, it appears that each hair consists of a closed 

 sac or pouch, over the inner surface of which protoplasm 

 is spread in a thin layer. Even this represents a much 

 more advanced modification of the protoplasmic mass, but 

 yet the protoplasm still retains its power of indepen- 

 dent motion. Wave-like movements are seen to pass 

 over the mass of the protoplasm, and by this, just as in 

 the Amwbce, a current is apparently produced among 

 the granules. For a time the movement continues 

 in one direction ; then it suddenly ceases and begins 

 again in an opposite direction ; sometimes one cur- 

 rent separates itself into two, others unite, and so on. 

 If the protoplasm dies — and this may be artificially 

 caused by the application of heat — all motion ceases. 

 It is inseparably bound up with the vital powers of the 

 cells. 



6. The free protoplasmic mass, as seen in the 

 Amoeba, is one of the simplest of organic forms. Such 

 masses sometimes occur in groups, which thus repre- 

 sent colonies of organisms, each of the components 

 of which, however, retains complete independence, 

 and is exactly like every other. Sometimes, however, 

 modification takes place amongst these ; and when 

 these modifications advance at an unequal rate in 

 the separate members of the colony, a composite or- 



