57 



mention the secretion by spons^es and diatoms of silica (en element 

 rare in sea water) in such great Quantity as almost to exhaust the 

 water of it; the ability of sea weeds to draw iodine and potassium 

 from the surrounding water so much more efficiently than man can, 

 that is is far more econoraicsl to obtain these substances from the 

 ash of sea weeds than it would be to concentrate them direct from 

 the water by any method yet perfected, or likely to be dt;Vclop-.d. 

 If any sea weed made equal use of gold, the extraction of gold from 

 sea water (in which on the av^^-rage there are about 5 mgra. p.r cubic 

 meter) v/ould not be th. will-o-the-wisp it has actually proved. k 

 more familiar example of th-r ability of tho living cell to s^lcCt 

 particular substances from the outside is the secretion of limy 

 shells by a great variety of plants and animals, an ability respon- 

 sible for vast deposits of calcareous sediments, of lim.estone rocks 

 and of the modern coral reefs. 



Why is it the organisms withdraw more lime in hin:h temperatures 

 and shoal water, more silica in low temperatures and in the deeps? 

 The chem.ical reactions that have been proposed to account for this 

 do not wholly explain it. 



The degree of p^rm-aoility of membranes for differ^^nt solutions 

 also holds the key to the riddle whether marine animals can feed 

 direct on the organic substances in solution in the water that have 

 not yet been reduced to their constituent nitrates, carbonates, etc. 

 The theory that they do so (the so-called "?utt-r's" th-ory) has 

 been much discussed, but is still op^n. 



This, too, introduces the whole qu:-stion of basic nutrition; such 

 as the natuTrr of the substances in the oil of copepods and diatoms, 

 and of the carbohydrates of unicellular marine plants, which, in the 

 words of on.; contributor, form "the daily fare of most thinsrs in the 

 sea. " 



A.llied to this is the question of the selection, oy different 

 vegetable cells, of specific solutes for their nourishment, or of 

 the sam.e solutes in different proportion. The vital mechamism back 

 of this selectivity (perhaps the most fundamental of all the peculi- 

 arities of living suDstance) is still a mystery to us. But thouerh 

 its solution (akin to the solution of life itself) may never be 

 reached, it is certain that its manifestations can be most directly 

 studied in the sea, where, for example, we often find one 0:roup of 

 unicellular plants thriving in water that some oth-r ccroup^had 

 already rendered barren for its-df by denuding it of the chemical 

 on which it subsisted. 



ic; 



In fact, the whole range of phinomena associated with th^ 

 specific affinity of these simpl, organisms for particular substanc-s 

 is best studied in th.; sea wher-^ is is carried out on a lare-r scale 

 by the simplest organisms. And such studi-s off:'r th.-: best oppor- 

 tunity, now in sight, to learn how it is that our own body cells 

 select one substance or another from our own food vi'^ the blood 

 stream, a question about wnich we are still almost wholly in the 

 dark. 



In a broader a?peGt, adds one contributor, is it, after all, 

 inherent character of living substance thst the specific chemical 

 solution we call sea water should prove so much more favorable an 



an 



