SALTS 441 



is one of a special group of elements. It is difficult to distinguish 

 between what is chemical and what is physical, yet it may be 

 said that in physical properties (electrostatic effects determined 

 by sign of charge and valency), any element within a group 

 (monovalent, divalent, etc.) will often serve as a substitute for 

 any other in the same group, but in its chemical (nutritional) 

 requirements, an element has no substitute. The plant demands 

 calcium, boron, or manganese and not a near relative of it. 

 Not only in nutrition but also in their effects on protoplasm, 

 substitution among the elements is not always possible. The 

 presence of calcium in the water makes healing of the cell mem- 

 brane possible owing to the coagulating effect of this element. 

 Magnesium will not replace calcium in this respect. The ques- 

 tion of substitution is part of that of antagonism. 



Antagonism. — Magnesium is necessary for plant growth, 

 yet it may, when certain other elements are not present in 

 sufficient quantity, produce "magnesium injury." This was 

 investigated by Tottingham and Trelease. The symptoms of 

 magnesium injury of wheat are so conspicuous and distinctive 

 that the disease furnishes a striking example of growth derange- 

 ment resulting from a disturbed salt nutrition. Trelease has 

 shown that calcium added to the nutrition of a plant in sufficient 

 quantity will prevent the injury caused by magnesium. The 

 occurrence and severity of the injury are determined by the 

 ratio of magnesium to calcium. The prevention of magnesium 

 injury by calcium is an example of what is known as salt antago- 

 nism. The role of calcium in this case is primarily physical, 

 as the injury is due to magnesium toxicity and not to calcium 

 deficiency. This is supported by the observation that strontium 

 is also able to delay and partially inhibit the characteristic 

 symptoms of magnesium injury. Such instances are ones where 

 substitution among elements of a group is possible. 



The antagonistic action of salts has furnished an interesting 

 and little understood chapter in physiology. It was discovered 

 by Ringer when he observed that the addition of calcium to a 

 common salt solution made the latter a better fluid for the 

 perfusion of the heart, not only because the element calcium was 

 needed by the tissue but also because a partial toxic effect of the 

 pure sodium was counteracted. J. Loeb continued the study 

 of antagonism. 



