CIRCUMSTANCES INFLUENCING CILIARY MOTION. 205 



the cilia communicate to the fluids or other matters in contact with them, maintains a con- 

 stant direction ; unless in certain of the lower animals, in which the motion is often variable 

 and arbitrary in direction, and might even be supposed to be voluntary. Thus in the windpipe 

 of mammalia, the mucus is conveyed upwards towards the larynx, and, if a portion of the 

 membrane be detached, matters will still be conveyed along the surface of the separated 

 fragment in the same direction relatively to that surface, as before its separation. 



The persistence of the ciliary motion for some time after death, and the regularity with 

 which it goes on in parts separated from the rest of the body, sufficiently prove that, with the 

 possible exceptions alluded to, it is not under the influence of the will of the animal, nor 

 dependent for its production on the nervous centres, and it does not appear to be influenced in 

 any way by stimulation or sudden destruction of these centres. The time during which it 

 continues after death or separation differs in different kinds of animals, and is also materially 

 influenced by temperature and by the nature of the fluid in contact with the surface. In 

 warm-blooded animals the period varies from two or three hours to two days, or even more ; 

 being longer in summer than in the cold of winter. In frogs the motion may continue four 

 or five days after destruction of the brain and spinal cord ; and it has been seen in the gullet 

 of the tortoise fifteen days after decapitation, continuing seven days after the muscles had 

 ceased to be irritable. 



Variations of temperature exert a very marked effect upon the rate and vigour of the 

 motion of cilia. Thus, in warm-blooded animals it is altogether stopped if the tempera- 

 ture is lowered to 6C., whereas, in cold-blooded animals, such as the frog and mussel, it goes 

 on unimpaired at 0C. The motion which has become quiescent from cold, may be revived by 

 warmth, and becomes more active in proportion to the rise in temperature up to a certain 

 point, which differs in warm and cold-blooded animals. In the former, this maximum tem- 

 perature is about 45C. ; above this the movement quickly ceases, the cilia passing into a 

 coagulated stiffened condition, known as heat-rigor, and which, if well marked, is not recovered 

 from. The temperature of the body seems to be that which is most favourable to the action 

 of the cilia ; that is to say, they will, if removed from the body, work vigorously for a longer 

 time at this temperature than at any other. 



Cilia will continue to work for a time in the absence of free oxygen. This was shown by 

 Sharpey, who noticed the movement of the cilia upon the gills of the tadpole to proceed for 

 some hours, even when immersed in water which had been deprived of its oxygen by boiling. 

 This experiment shows that like the substance of muscle, the protoplasm of the ciliated 

 epithelium-cell can store up oxygen in a combined form for future use. 



The immediate action of water is to increase the activity of cilia. Agents or conditions, on the 

 other hand, which abstract water from the tissue, retard or arrest the action. Thus most of the 

 common acid and saline solutions when concentrated arrest the action of cilia instantaneously 

 in all animals, but dilution delays this effect, and when carried far enough, prevents it alto- 

 gether. Fresh water soon arrests the motion in marine animals ; but it evidently acts by 

 destroying the epithelium-cells, which in these cases are adapted to a different medium. 

 Even in air-breathing and fresh-water animals water has after a time the same action, pro- 

 vided the ciliated cells are detached, so that it can pass by imbibition into their protoplasm. 

 Solutions of potash or soda, if extremely dilute, act like water, but more powerfully. 

 Virchow observed that a diluted solution of either potash or soda would revive the 

 movement of cilia after it had just ceased. The vapour of chloroform arrests ciliary action, 

 but the motion revives again if the application of the vapour is discontinued (Lister). 



Carbonic acid gas resembles chloroform in its action, rapidly arresting the movement if 

 conveyed over a ciliated surface, but the action speedily recommences on again admitting air. 

 The passage of the gas is, however, generally found to stimulate the movement at first. 



Bile stops the action of cilia, while blood prolongs it in vertebrated animals ; but the 

 blood or serum of the vertebrata has quite an opposite effect on the cilia of invertebrate 

 animals, arresting their motion almost instantaneously. 



It was noticed by Steinbuch that a mechanical stimulus, insufficient to injure the cilia, 

 such as that produced by the impulse of a current of fluid, acts markedly in exciting the 

 activity of ciliary motion. 



Electric stimulation, unless it causes injury to the ciliated surface, produces no obvious effect. 



Whatever views are entertained concerning the nature and source of the power by which 

 the cilia act, it must be borne in mind that each ciliated cell is individually endowed with the 

 faculty of producing motion, and that it possesses in itself whatever organic apparatus and 

 whatever physical or vital property may be necessary for that end ; for single epithelium cells 

 are seen to exhibit the phenomenon long after they have been completely isolated. 



Historical. Ciliary movement was first noticed (in the mussel) by de Heide in 1683, the 

 movements of spermatozoa having been previously discovered by Ham and Leewenhock. Sub- 

 sequently the movements were noticed in various situations. A comprehensive account of the 

 structure, distribution, and mode of action of cilia was given by Sharpey in the article " Cilia," 

 in Todd and Bowman's Cyclopasdia. That article, which appeared in 1835, was the result of 

 much laborious investigation, and still forms the basis of our knowledge .on the subject. 



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