Ixii CILIATED EPITHELIUM. 



way by stimulation or sudden destruction of these centres. The time 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 the destruction of the brain ; 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. 



With the view of throwing further light on the nature of this remarkable 

 kind of motion, experiments have been made to ascertain the effect produced 

 on it by different physical chemical and medicinal agents ; but, so far as 

 these experiments have gone, it would seem that, with the exception of 

 moderate heat and cold, alkaline solutions, chloroform vapour, and perhaps 

 some other narcotics, these agents affect the action of the cilia only in so 

 far as they act destructively on their tissue. 



The effect of change of temperature is different in warm and in cold-blooded animals. 

 In the former the motion is stopped by a cold of 43 F., whereas in the frog and river 

 mussel it goes on unimpaired at 32 F. E. H. Weber has made the interesting 

 observation that, in ciliated epithelium particles detached from the human nasal 

 membrane, the motion which has become languid or quiescent from the cold may be 

 revived by warmth, such as that of the breath, and this several times in succession. 

 A moderately elevated temperature, say 100 F., does not affect the motion in cold- 

 blooded animals ; but, of course, a heat considerably higher than this, and such as to 

 alter the tissue, would put an end to it in all cases. Electric shocks, unless they 

 cause abrasion of the ciliated surface (which is sometimes the case), produce no 

 visible effect ; and the same is true of galvanic currents. Fresh water, I find, 

 arrests the motion in marine mollusca and in other salt-water animals in which 

 I have tried its effect ; but it evidently acts by destroying both the form and sub- 

 stance of the cilia, which in these cases are adapted to a different medium. Most of 

 the common acid and saline solutions, when concentrated, arrest the action of the 

 cilia instantaneously in all animals ; but dilution delays this effect, and when carried 

 farther, prevents it altogether ; and hence it is, probably, due to a chemical altera- 

 tion of the tissue. Virchow has observed that a solution of either potash or soda 

 will revive the movement of cilia after it has ceased. Narcotic substances, such as 

 hydrocyanic acid, salts of morphia and strychnia, opium and belladonna, are said by 

 Purkinje and Valentin to have no effect, though the first-named agent has certainly 

 appeared to me to arrest the motion in the river-mussel. In confirmation of an 

 observation of Professor Lister,* I find that exposure for a few moments to the 

 vapour of chloroform arrests ciliary action, and that the motion revives again if the 

 application of the vapour is discontinued. 



Bile stops the action of the 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 must be confessed that the nature and source of the power by which 

 the cilia act are as yet unknown ; but whatever doubt may hang over this 

 question, it is plain 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 insulated. 



Without professing to offer a satisfactory solution of a question beset with so much 

 difficulty, it seems, nevertheless, not unreasonable to consider the ciliary motion as 



* Phil. Trans. 1858, p. 690, where will be found other valuable observations en the 

 effect of external agents on ciliary action. 



