130 Dr George Wilson on the Artificial 



e 



" that the experiment of manufacturing sea water for the 

 aquarium has been perfectly successful." 



In spite of this success, however, there are cogent reasons 

 for believing that sea water made according to the recipe 

 given above, would fail to maintain for any length of time 

 either plants or animals in health and vigour. 



Mr Gosse's sea water differs from that of the ocean in not 

 containing several ingredients which must be regarded as 

 essential to the growth of sea plants, and still more of sea 

 animals. It contains only such of the constituents of the 

 ocean as are soluble in pure water, and only some of these. 

 Thus, although it may be difficult or even impossible to de- 

 tect in considerable volumes of natural sea water, carbonate of 

 lime, sulphate of lime, phosphate of lime, fluoride of calcium, 

 and silica, all of these as well as oxide of iron are procured 

 in manifest quantity by evaporating sea water to dryness, as I 

 have many times ascertained by analysing the hard crusts from 

 the boilers of steam-ships, sailing in the Atlantic and German 

 oceans, and in the Mediterranean and other seas. The sul- 

 phate of lime and fluoride of calcium are soluble in pure water, 

 and the carbonate and phosphate of lime are kept in solution 

 by carbonic acid. The silica is either held simply in solution, 

 or occurs as a soluble alkaline silicate. 



Now it is plain that marine animals (to restrict ourselves 

 to them) must derive all their constituents, directly or in- 

 directly, from the medium in which they live ; and the law 

 does not appear to admit of any question, that whatever sub- 

 stances are invariably found in the structures of animals, 

 must be essential to their healthy development, and this 

 whether the substance is present in large or small quantity, 

 provided it is invariably present. Thus, to take one example, 

 we find fluoride of calcium, not isolated in one minute portion 

 of an animal's body, but built up along with phosphate of lime 

 wherever that occurs. It seems a dangerous rule to go 

 by, that because the quantity of fluoride is much smaller than 

 that of phosphate, the fluoride may be ^omitted altogether. 

 We might as well, I apprehend, in erecting a house, dispense 

 with mortar, because the quantity used in building is very 



