EFFECT OF IONS ON GROWTH 105 



not only of the toxicity of one of the ions, but of 

 antagonism between a monovalent and a divalent 

 metallic ion. An opposite effect of these ions upon 

 medusae was observed ; the bell continuing to con- 

 tract in a pure solution of NaCl after removal of the 

 nervous system, and ceasing to contract when 

 calcium or strontium was added ; again, however, 

 witnessing to the antagonism between the ions. 

 Ciliary action is also stimulated by one and de- 

 pressed by the other. The excised gastrocnemius 

 of the frog is stimulated to contract by pure sodium 

 chloride solution and checked by calcium or stron- 

 tium ; while, on the other hand, pure solution of 

 sodium chloride is toxic to heart muscle, and 

 calcium or strontium is antitoxic. 



Extended observations of the effects of ions on 

 heart tissue were made by Knight.* The experi- 

 ments were upon the embryos of perch and Fundulus. 

 The general result of the observations was that 

 chlorides of the metals depress the heart beat ; but 

 the degree of the depression depends upon the kind 

 of metallic ion. Heavy metals like Cu and Au 

 caused the beat of the heart to fall gradually until 

 it ceased beating, the ventricle ceasing first. Lighter 

 metals such as K, Na, Li, Cs were also used. Potas- 

 sium and caesium chlorides acted as heart depres- 

 sants, the cation K being more energetic, and the 

 auricle continued to beat a few times after the 

 ventricle ceased to contract. Calcium and strontium 

 stimulated the contractile efforts of the heart ; while 

 Mg, Ba, Be, Zn, and Cd acted as depressants. The 

 addition of calcium chloride to the solution always 



* Brit. Med. Jour., 1897, ii., 1484. 



