588 



STUDIES IN GENERAL PHYSIOLOGY 



It seems as if the physical condition of the colloids was the 

 essential point, and that this might be affected by various 

 ion combinations in the same way. 



Solutions which alloio the formation of a skeleton. The 

 next question was what ions should be added to the above- 

 mentioned solutions in order to obtain plutei with a skeleton. 



FIG. 147 



I found that a trace of Na 2 CO 3 has that effect. In a solu- 

 tion of 95 c.c. f nNaCl + 2 c.c. y> n CaCl 3 + 1 c.c. f n KC1 

 -f- 1 c.c. ^n NaCO 3 a skeleton was formed within three days. 

 This skeleton was not quite normal. It showed a formation of 

 knobs and spheres which I never saw in the skeleton formed 

 in normal sea-water (Fig. 147 B). I was anxious to obtain 

 plutei with normal skeletons, and succeeded in doing so by 

 adding a trace of MgCl 3 to the above-mentioned solution. 

 The solution which yielded plutei with a normal skeleton con- 

 sisted of 95 c.c. f n NaCl + 1 c.c. ^ n M-C1 3 + 1 c.c. fn 

 KC1 + 2 c.c. y>, CaCl 3 + 1 c.c. J Na g CO 3 . The skele- 

 ton is sketched in Fig. 147, A. It was therefore evident that 



