21 



He determined also the amount of iodine in sea water to be 2.32 mgr. 

 per liter.i Various marine organisms contain moderately large quan- 

 tities of iodine. For instance, Harnack isolated iodospongin, containing 

 on an average 8.2 per cent iodine, from marine sponges. 



DrecliseP found in a protein, viz, tlie axial horny skeleton of the 

 coral Gorgonia cavoUnii, 7.7 -per cent iodine. On decomposition with 

 baryta this protein yields a compound of the composition of mono- 

 iod-amido-butyric acid. Potassium or sodium iodid, even in small doses, 

 exerts a poisonous influence on animals as well as on plants. Germi- 

 nating buckwheat seeds placed in a full mineral solution in which the 

 potassium was offered as iodid, died before the first leaf was developed, 

 as the writer observed many years ago. The poisonous action of the 

 iodid of potassium is no doubt due to the liberation of iodine by oxida- 

 tion favored by the acid cell sap. Lower organisms without acid juices 

 are rather indifferent in this respect. The writer found certain algae and 

 infusoria alive in culture water five weeks after 0.5 per cent of iodid of 

 potassium had been added to it. On the other hand, 0.2 per cent 

 potassium iodid killed larger kinds of ^inrogyra within a few days 

 when the culture solution contained traces of the acid mouopotassium 

 I)hosphate. Lower fungi and bacteria are not injured in neutral culture 

 solutions to which even 1 per cent of this iodid is added. Potassium 

 iodid has been found by bacteriologists to possess a germicidal action 

 only when present in large doses. 



THE PHYSIOLOGICAL ROLE OF ALKALI SALTS. 



IMPORTANCE OF POTASSIUM FOR THE FORMATION OF STARCH AND 



PROTEIN. 



The paramount importance of potassium salts for every living cell is 

 firmly established. In green plants they are concerned not only in the 

 synthesis of carbohydrates, but also in that of the protein bodies, since 

 not only is there an increase of potassium salts in such parts of green 

 plants as are developing rapidly and consequently forming large 

 amounts of i)rotein, but most fungi, even in the presence of such a 

 favorable nutrient as sugar, are found to require potassium salts for the 

 production of protein. These salts can never be replaced by lithium-^ 

 or sodium salts, but in certain fungi they may be replaced to a limited 

 extent by rubidium or caesium salts (p. 25). 



It is a well-known fact that plants cultivated in the presence of more 

 sodium than potassium salts will nevertheless absorb a greater quan- 

 tity of the latter than of the former, and some plants grown on soil 



' A part of this iodine is present in organisms and organic compounds. 



^Zeitsch. f. Biologie, 1895, Vol. XV. Drechsel calls this protein "gorgonin." On 

 decomposition it yielded not only iodine, but also 2 per cent chlorine (or bromine?). 



•VA.1 though lithium salts exert a noxious action on Phanerogams they do not readily 

 affect algSB. Spirogyra still appeared normal after four weeks in a complete culture 

 solution to which 0.3 per mille lithium chlorid was added. At a higher concentra- 

 tion, however, the result may differ. 



