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Mr. J. Gray. 



known to possess a limited amount of reserve chemical energy. The effect 

 of acid on such cells is precisely similar to that on ciliated cells (Gray, 13). 



Cohn(5) has shown that when the movement of such spermatozoa has 

 ceased in an acid medium, there is no loss of energy,* the conversion of 

 chemical into potential energy has ceased, and can be switched on again 

 by removing the acid from the external environment. It seems highly 

 'probable, therefore, that the movement of cilia is stopped in an acid medium 

 because there is no longer a conversion of chemical into 'potential energy. 



(b) Metallic Ions. 



We have already seen that the cilia of Mytilus beat normally in an 

 artificial solution containing ISTaCl, KC1, CaCl 2 and MgCU, and whose 

 hydrogen ion concentration is the same as sea-water. On the whole, ciliary 

 activity is remarkably independent on the absolute concentration of any 

 particular ion or upon the exact ratio between different ions. In an 

 investigation of the effects of individual ions it is necessary to maintain the 

 normal hydrogen ion concentration and also the concentration of other ions 

 in the solution. Further, in making a comparison between the effects of an 

 ion on ciliary and on muscular activity, comparison must be made to a 

 spontaneously contractile muscle (e.g., the auricle of the heart). These facts 

 explain the difference in the conclusions arrived at in this paper, and those 

 of Lillie(20), Hober (16) and Mayer (23). 



Experiments v;ith Potassium Chloride. — If KC1 be omitted from the external 

 medium and its place taken by NaCl, the lateral cilia come to rest. The 

 time taken for the movement to cease varies considerably in different gills. 

 In most cases movement slows down after 5-10 minutes, and in less than 

 20 minutes the cilia are stationary. In a few cases in which the lateral 

 cilia showed very active movement before the experiment, movement was 

 continued in the absence of potassium for as long as 45-60 minutes ; move- 

 ment recommences vigorously on the subsequent addition of potassium, or 

 on the addition of a small amount of alkali sufficient to raise the Pit to 

 about 8'5. It should be mentioned that in several cases the lateral cilia 

 ceased to beat in normal sea-water after about 1\ hours, but on addition 

 of a slight amount of KC1, vigorous movement took place. This may 

 possibly be due to the fact that the blood of the animal contains a higher 

 concentration of potassium than does normal sea-water, so that when isolated 



* E. G. Martin (22) found that, in the presence of alkali, spontaneously beating strips 

 of the ventricle of the tortoise gave out a constant total amount of energy for a UEit 

 mass of tissue. 



