28 THE THEORY OF IONS 



and found that in the presence of calcium and 

 potassium salts the impulses started in the margin 

 and were therefore of nervous origin ; from which 

 he concluded that the chemical rather than the 

 histological structure of the ganglia was important. 

 Howell* says the normal stimulus of contraction 

 depends upon the presence of calcium salts, but for 

 rhythmical contraction the presence of potassium 

 salts is also necessary. Loebf also considers that 

 calcium, potassium, or sodium salts do not form 

 the stimulus for rhythmical contraction in cardiac 

 and other contractile tissues, but that their presence 

 in the tissues in a definite proportion is necessary ; 

 if the proportion is not correct a rhythmical con- 

 traction does not take place. If the amount of 

 sodium chloride in it is too small, it may be in- 

 creased by placing the tissue in a solution of pure 

 NaCl, and a rhythmic action will then be brought 

 about ; if the calcium chloride is too small increasing 

 it in the same manner will initiate contraction. J 

 All contractile tissues do not require the same 

 chemical constitution or environment. Thus, 

 potassium alone annihilates muscular contraction 

 rapidly ; but ciliary activity, which is considered to 

 be a protoplasmic action of the same order, and cell 

 division will continue in the presence of enormous 

 quantities of potassium salts. 



A similar discussion has arisen about the action 

 of the heart, and has partly taken place from the 

 standpoint of ionic dissociation. Attempts, con- 

 sidered by many authorities to be successful, have 



* Amer. Jour. PhysioL, 1898, ii., 47. 

 t Loc. cit. Loc. tit. 



