SECTION II 

 PHYSIOLOGY OF MUSCLE AND NERVE 



CHAPTER III 

 MOTION 



Different Types of Motion. The phenomenon of contractility 

 consists in a shifting about of the constituents of the cell. It may 

 be perfectly local or more far reaching, leading finally to changes in 

 the shape and position of the organism as a whole. In this way, this 

 liberation of energy gives rise to motion and locomotion, phenomena 

 which the layman regards as the most certain proofs of life. The 

 character of these movements is very manifold and is in keeping 

 with the general structure and arrangement of the motor organs pro- 

 ducing them. In general, it may be said that motion may be accom- 

 plished either passively or actively, in consequence of the following 



processes: 1 



Motion 



A. Passive 



( Swelling of the cell wall 



Changes in the cell-turgor 

 TJ . I Changes in the specific gravity 



Jj. ./VC LlVG i ci i_ 



1 Secretion 



Growth f ameboid 



Contraction and expansion j ciliary 



I muscular 



A passive motion results whenever the power to move is not inherent in the 

 object. Thus, if we observe the circulation of the blood under the microscope, the 

 erythrocytes are seen to traverse the vascular channels with a certain speed, but 

 this movement is imparted to them byanoutsideforceresidentin the musculature 

 of the heart. We may also study the streaming of the protoplasm in such organ- 

 isms as the rhizopods. We note here the slow progression of the granules to and 

 from the cells, but they themselves are quite inactive and move solely in conse- 

 quence of the flow of the medium in which they are contained. In this connection, 

 mention should also be made of the so-called Brownian molecular motion which is 

 displayed by many plant cells, and lower organisms. A very favorable object 

 for observation is the unicellular green alga, called closterium (Fig. 6, I) which 

 contains in each end of its crescent-shaped body a vacuole filled with fluid and fine 

 granules (K). If the latter are observed under the high power of a microscope, 

 they are seen to be engaged in an incessant trembling motion. The same pheno- 



1 Verworn's Allg. Physiol., Jena, 1909, and Winterstein's Handb. der allg. 

 Physiol., Jena, 1912. 



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