The Mechanism of Ciliary Movement. 



127 



concentrations, the tissue does not remain so healthy as in that containing 

 magnesium and sodium ; in the former solution there is a distinct tendency 

 for the finer cilia to become opaque and detached from the cell : this is 

 particularly the case with the small cilia on the ciliated junctions, so that 

 individual gill filaments show a distinct tendency to separate from each 

 other (see Gray (3)). Interesting facts concerning the action of calcium are, 

 however, available from a study of cells whose normal semi-permeability 

 has been destroyed by immersion in those sodium salts which prevent the 

 uptake of an abnormal amount of water by the cell. When ciliary move- 

 ment has ceased in sodium citrate, the cilia and the tissue appear quite 

 healthy and translucent. On transference to normal sea-water, however, 

 the cilia at once become opaque, and are completely destroyed ; at the same 

 time there is a rapid uptake of water by the cells which swell up in the 

 usual way. If, on the other hand, the tissue (after initial citrate treatment) 

 be placed in sea-water containing no calcium, the cells and cilia remain 

 quite healthy, and complete recovery of movement takes place, although 

 the rate of beat is usually slower than the normal ; after a time the rate 

 of beat falls off, but can be revived permanently by adding calcium. The 

 same recovery from sodium citrate treatment can be effected by treating the 

 tissue with any solution containing magnesium but no calcium. The same 

 experiments can be performed with tissues previously treated with sodium 

 sulphate or sodium tartrate. It is clear from numerous experiments that 

 magnesium is the only ion in sea-water which will re-form a semi-permeable 

 membrane round a cell which has lost this structure by exposure to a pure 

 sodium salt. 



At this point it is interesting to note that calcium has a double action 

 on ciliated cells : (a) It is capable of maintaining the cell surface in a normal 

 state of semi-permeability ; (b) it is necessary for continuous movement in 

 a solution of Ph 7*0 (see Gray (5)). In the first of these functions calcium 

 can be completely replaced by magnesium, but cannot be so replaced in 

 the second. 



The destructive effect of sodium salts upon the cell membrane is shared 

 by other monovalent cations, although to a variable extent. In the case of 

 the chlorides, there is little difference between Na', NLV, and K', while 

 the effect of Li' is considerably less. In the case of other salts, e.g., tartrates 

 and citrates, the erosive power of the potassium salts appears to be distinctly 

 less than that of the corresponding salts of sodium. Pure solutions of 

 magnesium and calcium salts have no erosive action for a considerable time 

 (six to eight hours), after which the cell membranes begin to be affected. 



It is curious to notice that magnesium has little or no stabilising action 



