74 



THE AMERICAN MONTHLY 



[April, 



Hum or to the same ciliated surface 

 are not isochronous, as they are in 

 the single cell, the}' are repeated 

 with equal frequency and are defi- 

 nitely successive ; this gives rise to 

 the often quoted wave-like appear- 

 ance, which, as it runs over the 

 ciliated surface, suggests the move- 

 ments of a field of grain in a strong 

 wind. This phenomenon is micro- 

 scopically apparent in the cteno- 

 phora. The direction of these waves 

 is quite constant, but may suddenly 

 change to the opposite direction, in 

 consequence of the cilia reversing the 

 direction of their more forcible strokes, 

 as we have already noted. The velo- 

 city of the waves is directly in accord 

 with the frequency of the oscillations, 

 and therefore dependent to a marked 

 degree upon external conditions. 



For the purpose of estimating the 

 velocity of the cilia-propelled cur- 

 rents, and the force exercised, several 

 ingenious methods have been em- 

 ployed. The velocity of the current 

 is only to be measured by very easily 

 moved bodies placed upon the mem- 

 brane ; for this purpose a strip of 

 ciliated mucous membrane is scretched 

 out to its normal length and breadth, 

 and the time required for a light body 

 {e.g., a bit of sealing wax, suspended 

 by a thread from a cocoon) to pass 

 over a certain distance is calculated 

 by means of a metronome. The ap- 

 paratus used in this method has been 

 designated the "ciliary-clock." An- 

 other, the "ciliary-mill," consists of a 

 light cylinder carrying a swinging 

 index, which is placed upon the mem- 

 brane. One revolution of this cylin- 

 der is indicated by means of the 

 passage of an electric spark through 

 regularly arranged apertures in an- 

 other cylinder covered with blackened 

 paper. From the intervals between 

 the marks made by the sparks, and 

 the known rapidity of rotation of the 

 paper covered cylinder, is indicated 

 the angular velocity of the axis, which 

 may be considered as a measure of 

 the velocity of the current. 



By these two methods the velocity 



has been calculated to be, from 4 to 

 24 mm. a minute. Compared with 

 muscular strength, the energy ex- 

 hibited by cilia in bending themselves 

 is very great. Thus Wyman found 

 that 48 grms. could be moved along 

 when brought in contact with 14 

 square mm. of ciliated surface, and in 

 the experiments of Bowditch the 

 loaded surface carried along 6.805 

 gramm-millimeters per cubic centi- 

 meter per minute.* When it is re- 

 membered that only the basal portion 

 of each cilium performs the work, it 

 will be better understood how great 

 is the force compared to that of the 

 heart. Thus Bowditch calculated 

 that every cell could, at the maximum, 

 raise a weight equalling its own, to a 

 height of 4.253 metres in one minute. 

 Cilia, with the exception, perhaps, 

 of seminal filaments, move themselves 

 only so long as they remain in con- 

 nection with their proper cell-bodies. 

 Yet it would seem that it is only that 

 portion of the cell protoplasm situated 

 about the bases of the cilia which 

 serves for the maintenance of motion. 

 Engelmann observed the liveliest 

 movements in the cilia of the gills of 

 an oyster in which the nucleus-bear- 

 ing half had been accidentally sepa- 

 rated from the cilia-bearing portions. 

 We may often see in infusoria which 

 have been mangled, or are under- 

 going dissolution, a single cilium, to 

 which a small portion of the body- 

 substance remains attached, continue 

 in active movement for a long time. 

 On the other hand, the tails of many 

 spermatozoids move themselves when 

 completely separated from their 

 bodies, approaching in this respect, 

 as in many others, ordinary proto- 

 plasmic (ibres.* From these facts we 

 are inclined to doubt the theory that 



* Engelmann recommends the use of the 

 mucous membrane of the palate and oesopha- 

 gus of the frog in measuring the power of 

 cilia. 



* Tlie large ])ectinaled cilia of ciliograde 

 acalepha continue in the same manner their 

 movements in parts severed from the body 

 (R. E. Grant). 



