56 THE INORGANIC CONSTITUENTS OF MARINE INVERTEBRATES. 



Our determinations of magnesia, however, are subject to at least one small correction. 

 Many of the specimens analyzed contained inclosed or adherent sea salts, and in a few ol them 

 they could not be estimated. They rarely amounted to more than 2 per cent, but in one analysis 

 5 per cent was found. Sea salts contain magnesium, and its ec|uivalent in magnesium carbonate 

 must therefore be deducted from the percentages of magnesium carbonate given in our reduced 

 analyses. The maximum correction to be thus applied is about 0.4 per cent, but 0.1 per cent 

 would be the more common amount. In our work such a correction is negligible, for the pro- 

 portion of magnesium carbonate in our important magnesian series ranges from 5 to 25 per 

 cent. The small cjuantities of maghesia found in most mollusks and corals, however, maj' be 

 due in part, if not entirely, to saline impurities. 



Phosphorus. — In nearly all our analyses phosphoric o.xide appears, but generally in trifling 

 quantities. It is abundant, however, in the series of phosphatic brachiopods, the crusta- 

 ceans, and the alcyonarians. Some worm tubes also are notably phosphatic. In reducing the 

 analyses to standard form we have assumed that the phosphoric oxide is best represented 

 in combination as tricalcium phosphate, although the assumption is not absolutely proved. 

 It is a pure convention, adopted for the sake of uniformity and to simplify the comparison 

 of analyses. It is of course possible that magnesium phosphates may exist in some of the 

 organisms and that a part of the phosphorus may be contained in their organic matter. Mag- 

 nesium phosphates, however, are very rare as minerals, whereas calcium phosphate is 

 extremely common. The organic matter decomposes after the death of the animals, and its 

 phosphorus would doubtless appear in the sechments as a phosphate. In any case the dead 

 organisms are likely to be buried among calcareous sediments, where calcium phosphate should 

 Be formed. Even the phosphatic worm tubes, in which the calcium is insufficient to form a 

 tribasic salt, would probably follow this rule. Lime from the sediments would supply the 

 deficiency. 



Sulphur. — In many of our analyses sulphur was determined as sulphur trioxide and recal- 

 culated into the form of calcium sulphate. Part of the sulphur may really exist in organic 

 combination, especially in the phosphatic bracluopods, and another part maj- be derived from 

 sea salts, but this part is extraneous and should not be considered as contributory to the sedi- 

 ments. A correction for it would be like that which we have regarded as applicable to the 

 magnesia and of the same order of magnitude. In the marine sediments generally calcium 

 sulphate is of minor importance. 



Other constituents. — Among the inorganic constituents of invertebrates there are other 

 elements than those which we have determined. The most important one of these is fluorine, 

 which is probably present in small amount in all living organisms. P. Carles,^* for example, 

 has detected fluorine in the shells of mollusks — as much as 0.012 per cent in oyster shells. In 

 combination with calcium phosphate fluorine may form a compound analogous to or identical 

 with apatite. Its presence in vertebrate bones is well known. Boron also is widely distrib- 

 uted in the animal kingdom. G. Bertrand and H. Agulhon ^' detected it in crustaceans, 

 mollusks, and ecliinoderms, as well as in vertebrate animals. Traces of barium have been 

 detected in various organisms, and in the soft part of certain rhizopods granules of barium 

 sulphate have been found. ^^ Strontium is reported by O. VogoJ " in corals and molluscan 

 shells, and according to O. Butschli ^* the skeleton of a radiolarian, Podecanelius, consists 

 almost entirely of strontium sulphate. Iron and manganese are of common if not of general 

 occurrence in marine organisms, and copper, lead, zinc, cobalt, and nickel have also been 

 found.^' The presence of copper in oysters has long been known. Silver has been detected 



" Carles, P., Compt. Rend., vol. 144, pp. 437, 1240, 1907. 



» Bertrand, G., and Agulhon, H., idem, vol. 156, p. 732, 1913. 



« Cited by Samoilov in Mineralog. Mag., June, 1917. 



" Vogel, O., Zeitschr. anorg. Chem., vol. ,i, p. 5.i, 1894. 



M Butschli, O., Deutsche SUdpolar Exped., vol. 9, p. 237, 1908. 



» See Forchhanuner, G., Philos. Trans., vol. 15."), p. 203, 1865. 



On manganese see Cotte, J., .Soc. biologic Compt. rend., vol. .55, p. 139, 1903; Bradley, H. C, Jour. Biol. Chem.', vol. 3, p. 151, 1907, and vol. S, 

 p. 237, 1910: Boycott, A. E., Nattu-aUst, 1917, p. 69, and Phillips, A. H., Carnegie Inst. Washington Pub. 151, p. 89, 1917. Phillips also found iron, 

 copper, and zinc in the soft parts of invertebrates, and, rarely, lead. See also Mendel, L. B., and Bradley, H. C, Am. Jour. Physiology, vol. 14, 

 p. 313, 1905. For copper, .see Rose, W. C, and Bodansky, M., Jour. Biol. Chem., vol. 44, p. 99, 1920. 



