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Mr. J. Gray. 



in the presence of excess of potassium, and have contrasted this with 

 the depressant effect of such an excess on skeletal muscle. In view of the 

 effect of KC1 on the fronto-lateral cilia in preventing the recovery beat, it is 

 interesting to note that this is also its effect upon skeletal muscle, viz., the 

 latter is thrown into a state of prolonged contraction (Mines); the same 

 thing occurs in the vertebrate heart (Barridge, 3). 



The recent work of Kolm and Pick (18) on the effect of potassium on the 

 heart brings out clearly three points : (i) the marked quickening effect on the 

 automatically contractile auricles and sinus ; (ii) the differential action on 

 different tissues in the same organ, viz., auricles, ventricle ; (iii) the prolonged 

 contraction which is caused by high concentration of potassium : the con- 

 traction eventually passing off in the presence of the same perfusion fluid. 



As far as I am aware there is no evidence against the view that in the case 

 of automatically contractile tissues the effect of low concentrations of 

 potassium salts is to increase the rate of movement, while stronger concen- 

 trations cause a prolonged contraction which is not, however, permanent. 



The relative immunity of cilia as compared to a muscle cell to potassium is 

 probably due to the fact that the latent period of the cilium is very much 

 less than that of the average muscle cell, so that an environment which 

 throws the latter into tonic contraction by increasing the rate of activity of 

 the cell, has much less effect on the cilia. 



Tlie Effects of the Sodium Ion. — We have already mentioned that the 

 absolute concentration of Na can be raised considerably without deranging 

 ciliary movement. If the concentration of CaCl 2 , MgCl2, and KC1 be kept 

 constant, and the sodium chloride replaced wholly by isotonic saccharose, 

 ciliary movement is well maintained for several hours. 



It seems reasonable to conclude therefore that the sodium ion plays no 

 specific role in activity — although it probably enters into the conditions of 

 the general equilibrium within the cell. 



The Effects of the Magnesium Ion. — If magnesium be omitted from the 

 Van't Hoff solution., and its place taken by an appropriate amount of calcium, 

 ciliary action is well maintained for many hours (more than 48 hours). 

 Within wide limits a variation in the concentration of magnesium in the 

 medium has little effect upon the form or rate of beat of the terminal 

 cilia. 



This fact is in accordance with observations upon the heart of the Octopus 

 (Predericq), the arms of Lepas (Mayer), and the heart of Salpa (Mayer) — 

 all of which are insensitive to an absence of magnesium. The sensitivity 

 of the heart of Pecten (Mines) is doubtless correlated with its high sensitivity 

 to hydrogen ions (Mines). 



