ions act on the stability of the intercellular matrix. 

 Under normal conditions magnesium is essential 

 for the maintenance of stability. If the gill 

 preparation is placed in a medium containing 

 sodium and magnesium, the cells remain stable; 

 these deteriorate rapidly in a mixture of magnesium 

 and potassium. It is probable that the potassium 

 ion drives away magnesium from certain areas 

 inside the cell and sodium ions do not (Gray, 

 1922b). In the absence of calcium the rate of 

 ciliary beat is gradually decreased and eventually 

 ceases (Gray, 1924), but the increase of calcium 

 in the surrounding water produces no marked 

 effect on ciliary motion. 



As long as the normal equilibrium of tlie cations 

 sodium, potassium, calcium, and magnesium is 

 maintained in the surrounding medium, the ciliated 

 cells (of Mytilus) are insensitive to changes in 

 the concentration of anions (CI", NO3", Br , I , 

 acetate, and SO4 ). 



It may be assumed that the results of observa- 

 tions on Mytilus gills are applicable to the oyster 

 and that changes in the ionic equilibria in sea 

 water may have a similar effect on the efficiency 

 of the ciliated mechanism of oysters. 



HYDROGEN IONS 



The effect of variations in the concentration of 

 hydrogen ions on the rate of ciliarv' motion in 

 bivalve gills is greater than that caused by changes 

 in the concentrations of any other ions. This 

 lias been demonstrated on tlie gills of Anodonta, 

 Mytilus, Mya, and Ostrea (Chase and Glaser, 

 1930; Gray, 1928; Haywood, 1925; Nomura, 1934; 

 Yonge, 1925). The greatest effect is produced 

 by those acids which, like carbonic acid, penetrate 

 the cell surface most rapidly. Nomura (1934) 

 found the following order of efficiency of acids in 

 arresting the ciliary motion of Pecten: H2C03> 

 CH3COOH>H3P04'>HCl. Ciliary activity ceases 

 in 1 minute at pH 3.8 wlien IICl has been added, 

 but with CH3COOH or IL.COs the stoppage 

 would occur in the same time at the much higher 

 pH of 5.5. A decrease in the pH values of sea 

 water from 8.1 to 6.1 reduces the ciliary motion of 

 the gills of C. viniinica to about 37 percent of their 

 normal rate. In tliese observations by Galtsoft' 

 and Whipple (1931) the pH of sea water was 

 changed by bubbling carbon dioxide, and measure- 

 ments were made of tlie rate of flow of water 

 produced by the lateral cilia. Ciliarv motion 

 stops completely over the entire gill surface of 



the oyster when the pH of water is reduced to 

 5.3 to 5.6. Minimum pH in which the cilia can 

 function depends on the concentration with which 

 they are normally at equilibrium. This was 

 demonstrated clearly by Yonge (1925) on the 

 cilia of Mya. Thus the average pH inside the 

 style sac of this clam is 4.45 and the cilia of the 

 sac stop functioning below pH 3.5 to 4.0, while 

 the gill cilia normally surrounded by sea water 

 of about pH 7.2 come to a standstill at pH 5.2 to 

 5.8. 



VARIOUS DRUGS 



Tiie eft'ects of various drugs on ciliaiy motion 

 of the gill epitlielium of Anndonta, Pecten, Mytihis, 

 and Ostrea have been observed by various in- 

 vestigators. 



The reaction to any effective drug usually 

 takes place in four consecutive stages: (1) re- 

 tardation of the frequency of beat, (2) disappear- 

 ance of metaciironism along the ciliarv tract 

 and its perseverance within the individual cells 

 (unicellular metachronism), (3) synchronous beat- 

 ing of the cilia of a single cell (disappearance of 

 unicellular metachronism), and (4) cessation of 

 beat. 



The degree of depression depends on the con- 

 centration of the drug used and the duration of 

 its action. Cessation of beat in the gills of 

 Anndonta was observed in the following compounds 

 (Bethell, 1956): 0.5 percent chloral hytlrate (in 

 4 to 5 minutes) ; 1 percent novocaine (9 minutes) ; 

 1.5 percent pilocarpine hydrochloride (in 10 

 minutes). In 1 to 1.5 percent vera trine sulfate 

 the metachronal wave slows until movement 

 ceases. Caffeine (2 percent solution) accelerates 

 the ciliary motion for 3 minutes and in 6 minutes 

 completely depresses it. The effect of adrenaline 

 on the gills of C. (jieias was studied by Nomura 

 (1937). The rate of ciliary motion was observed 

 on excised oblong pieces of the gill that were 

 placed in a graduated, narrow glass tubing. 

 They crawled along the glass surface of the 

 tubing, and their advance during 1 minute was 

 recorded. The crawling velocity in various con- 

 centrations of adrenaline also was recorded, 

 and the degree of depression of ciliaiy motion 

 was expressed in percentage of the velocity 

 attained in natural sea water. The results show 

 that the ciliary movement is depressed in pro- 

 portion to the concentrations, which varied from 

 10-'° to 10-=^. 



Observations made in the Bureau's shellfish 



140 



FISH AND WILDLIFE SERVICE 



