MECHANICAL MOVEMENTS IN CELLS. 81 



dition is reached the normal condition of the cells may be again restored 

 through the use of desiccating agents, such as salts, which have an 

 affinity for water, provided the watery distension has not lasted too long, 

 nor has passed a certain degree. Abstraction of water again, on the 

 other hand, reduces the rapidity, amplitude, and mechanical force of 

 movement, while the cells and cilia become shriveled and motion is 

 arrested. Like all other evidences of protoplasmic activity, a certain 

 supply of oxygen is necessary for the maintenance of ciliary motion, 

 and here again the same conditions may be determined as will be 

 described under the conditions necessary for protoplasmic movement. 

 So also various chemical influences, alkalies, acids, anaesthetics, and 

 poisons produce disturbances of motion dependent upon their influence 

 on the protoplasmic contents of the cells. The influences of electricity 

 on ciliary movement have not been, as yet, very clearly made out, 

 although they also appear to be in accord with the results obtained from 

 the action of electricity on protoplasm. 



These facts serve to show that ciliary movement is a form of pro- 

 toplasmic movement ; for, not only is such motion dependent on the con- 

 nection of the cilia with the cell-contents, but all cilia on a single cell 

 vibrate synchronouslj', and their motion is dependent upon the condition 

 of the protoplasmic contents of the cells. Anything which interferes with 

 the manifestations of force in protoplasm will interfere with ciliary motion. 

 Ciliary motion, nevertheless, differs from other forms of protoplasmic 

 movement in that it occurs in definite directions, and, with the exception 

 of the spermatozoa and other ciliated organisms, on fixed surfaces. 



Cilia are contractile but not automatic or irritable, while the con- 

 tents of ciliated cells have apparently lost their power of independent 

 contractility. Cilia may, therefore, be regarded as the organs of move- 

 ment of certain cells. They, consequently, represent a certain stage of 

 specialization of function. 



3. Movement in Specialized Contractile Tissue. — In the contraction 

 of muscular tissue, specialization of function has advanced a step farther. 

 Free protoplasm originates its own stimulus to contraction, is therefore 

 automatic, and is itself contractile. In ciliated cells the contractile 

 impulse originates in the protoplasmic contents of the cells, which, how- 

 ever, have lost their power of contractility, and transfers the stimulus 

 to contractile organs, the cilia, which are not themselves automatic. 



In muscular tissue movement depends upon three histologically 

 different tissues : the nervous ganglion, which is automatic and originates 

 the contractile impulse ; the nerves, which conduct this impulse to the 

 muscles, which, like cilia, are contractile but not automatic. 



The phenomena of muscular contraction will be considered under 

 Special Physiology. 



