APPENDIX V 



Runnstrom regards his experiments with potassium-free sea water (19250) as indi- 

 cating that basal and ventral regions lose potassium more rapidly than other parts in 

 absence of external potassium and undergo more decrease in colloid dispersion. He con- 

 cludes that they are more permeable to potassium. His criteria of a ventrodorsal differ- 

 ential effect of lack of potassium are apparently based largely on individual cases of 

 somewhat modified development. 



The polar susceptibility gradient to lack of potassium is, according to Runnstrom, 

 acropetal in early cleavage. This is opposite in direction to the lethal gradients ob- 

 served by Child with various agents and to the dye reduction gradient, but if his 

 identification of ventral and dorsal regions is correct, the ventrodorsal susceptibility 

 gradient to lack of potassium is in the same direction as the lethal gradients and the 

 dye reduction gradient. 



Differential susceptibility to absence of potassium may perhaps involve other fac- 

 tors than those considered by Runnstrom. For example, there may be axial differ- 

 entials in distribution of potassium in the egg; or in its absence externally its internal 

 distribution may be altered by physiological factors, or there may conceivably be a 

 differential tolerance to loss of it and a differential recovery from its absence on return 

 to normal sea water. Withdrawal of an essential element such as potassium may have 

 effects very different from those resulting from addition to the medium of a toxic 

 agent. A susceptibility gradient to lack of potassium, whether it depends on differ- 

 ential permeability or on some other factor in the protoplasm, may have little relation 

 to the gradients indicated by nonspecific susceptibility to positive action of chemical 

 and physical agents or by dye reduction, and the effect may be still further compli- 

 cated by differential recovery after temporary exposure to potassium-free sea water, 

 the procedure in Runnstrom's experiments. Further experiment with a wide range of 

 potassium content, both above and below that of sea water and with different ex- 

 posure periods, appears desirable. 



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