20 LIVING AND LIFELESS MATTER 



poison to the organisms which secrete them, or to other animals 

 which absorb them in one way or another. 



MOVEMENT. Appearance and form thus cannot be unmis- 

 takable symbols of living matter. No mistake can be made, 

 however, if these two manifestations of vitality are taken to- 

 gether with a third and most important one, viz. movement. 

 A questionable object, if it has the characteristic form and 

 appearance of protoplasm and combines with these the power 

 of independent movement, may be safely interpreted as living 

 matter. Movement alone is not sufficient, for lifeless matter 

 may exhibit spontaneous movements of one kind or another. A 

 drop of water, for example, on a hot surface will move with 

 characteristic activity, or a piece of camphor on the surface of 

 clean water will dance about with considerable vigor, while 

 emulsions of oil, water, and salt will not only simulate the ap- 

 pearance of protoplasm but will also imitate the movements of 

 certain kinds of lower animals. In all of these cases, however, 

 movement is not spontaneous and independent, originating 

 from within the substance, but is due to surface tension or the 

 interaction of the more fluid water and the less fluid substance, 

 and is explained on purely physical grounds. Movement of 

 living things, while it may have at bottom some similar physi- 

 cal principle, is quite different for it originates through the 

 liberation of energy within the living substance. 



The types of movement of living things are quite varied but 

 they may all be referred to one or the other of the following 

 kinds: (i) flowing movement; (2) amoeboid movement; (3) 

 ciliary movement and (4) muscular contraction. 



Flowing Movement. The cells of the stone wort (Nitella) are 

 elongate units of structure with heavy walls of cellulose. With- 

 in the walls a steady streaming of granules can be made out. 

 This flow is confined to the layer of protoplasm around the 

 periphery of the cell just within the cellulose membrane, the cen- 

 ter of the cell being filled by a large vacuole containing water 

 which presses the living substance (primordial utricle) against 

 the walls. The protoplasmic flow is rendered visible by the 

 presence of larger or smaller granules and of "nuclei, " which are 



