III. 8 CHEMICAL COMPOSITION 145 



ii. Cl. 



A solution was made up in which the sodium chloride was 

 replaced by sodium formate, the magnesium chloride by magne- 

 sium sulphate, the potassium chloride by potassium sulphate; 

 thus, NaCOOH 3- 5 % + MgSO 4 -26 % + MgSO 4 -4% + K 2 SO 4 

 12 % + CaSO 4 -1 % + CaHPO 4 + CaCO 3 . 



The eggs did not segment, and even when KC1 and MgCl 2 

 were used in their ordinary proportions, segmentation did not 

 progress very far. Nor did the substitution of Na 2 SO 4 for 

 NaCOOH give any better results. A considerable amount of 

 chlorine appears therefore to be absolutely necessary for the 

 earliest developmental processes, its function being, Herbst sug- 

 gests, to transport certain necessary cations, the tissues being 

 possibly more permeable to NaCl than to Na 2 SO 4 . Later stages 

 blastulae, gastrulae, Plutei all die in the Cl-free mixture. 



Chlorine can be replaced in some measure by bromine. Plutei 

 are formed, though with a distorted skeleton, Tubularia regene- 

 rates its head and the eggs of the fish Labrax develop as well 

 as in sea- water. Iodine is, however, poisonous; so also are 

 chlorates. 



iii. Na. 



2-96 % of MgCl 2 was added to a solution containing the usual 

 amounts of KC1, MgSO 4 , CaSO 4 , CaHPO 4 , and CaCO 3 . In this 

 the ova indeed segmented, but abnormally, the blastomeres being 

 of unequal size. Death followed ; nor was the addition of a certain 

 small amount (-84 %) of NaCl sufficient to save them, though 

 segmentation was normal and traces of an archenteron could 

 be detected; with more NaCl (1-34%) the gastrula stage was 

 reached. The sodium which is thus necessary in the earliest 

 period is also required later on; without it gastrulation is im- 

 possible to eggs which have been reared in sea-water even as far 

 as the mesenchyme-blastula stage. 



The part played by sodium is not clearly understood. It 

 is known that it counteracts the evil effects of calcium and is 

 necessary for the continuance of muscular contractions. Since 

 calcium is necessary for the cohesion of cells (see below) Herbst 

 opines that sodium may pull them apart ; its action in that case 

 is capillary. 



JENKINSON It 



