PROTOPLASMIC MOVEMENTS. 



27 



know that living things are the seat of active changes, which 

 taken together constitute their life. In the last analysis these 

 changes are undoubtedly chemical actions taking place in the 

 protoplasm, which may or may not produce visible results. 

 There is no doubt that extensive and probably very complex 

 molecular actions go on in the protoplasm of young growing 

 cells, though it may appear absolutely quiescent to the eye, even 

 under a powerful microscope. In other cases, the chemical 

 action produces perceptible changes in the protoplasm, for in- 

 stance, some form of motion, just as the invisible chemical 

 action in an electrical battery may be made to produce visible 

 effects (light, locomotion, etc.) through the agency of an electrical 

 machine. 



A familiar instance of protoplasmic movement is the contrac- 

 tion of a muscle. This process is most likely a change of molec- 

 ular arrangement, causing the muscle, while keeping its exact 

 bulk, to change its form, the two ends being brought nearer 

 together (Fig. 16). The visible change 

 of form is here supposed to be due to an 

 invisible change of molecular arrange- 

 ment, and this in turn to be coincident 

 witli chemical action taking place in the 

 living substance. 



A striking and beautiful example 

 of movement in protoplasm occurs in 

 the simple organism known as Amoeba 

 (Fig. 84, p. 150). The entire body of 

 this animal consists of a mass of naked 

 protoplasm enclosing a nucleus, or 

 t sometimes two ; in other words, it is a 



Fio/i6.-change of form in a &&e aked cell. The protoplasm of 

 contracting muscle. A, mus- an ac tive Amceba- is in a state of cease- 



cle in the ordinary or extend- ,. 



ed state; B, the same muscle less movement, contracting, expanding, 



when contracted. (Diagram.) fl owmg? an( J changing the form of the 



animal to such an extent that it is known as the "Proteus.^ 

 animalcule. The whole movement is a kind of flux. A portion 

 of the protoplasm flows out from the mass, making one or more 

 prolongations (pseudopods) into which the remainder of the 

 protoplasm finally passes, so that the whole body advances in the 



