244 STUDIES IN GENERAL PHYSIOLOGY 
No regeneration whatsoever occurred in the first solution; 
in the second small abnormally formed polyps with tiny 
tentacles, which soon dropped off, developed. No growth 
occurred. 
5. Whether other substances can be substituted for NaCl 
I was not able to investigate at this time. If we omit this salt 
from our conclusions, our experiments show that a small 
amount of potassium must be contained in solution if the 
polyps are to regenerate, but that for the formation of normal 
polyps and for normal growth magnesium is also required. 
Besides NaCl (for which substitutes may perhaps be found), 
these two substances suffice for regeneration and growth in 
Tubularia.' In only one respect did the parts regenerated in 
my artificial solutions differ from those obtained in normal sea- 
water—the periderm of the former remained soft, while that 
of the latter became hard. The importance of potassium 
in the formation of cells has been emphasized by Hoppe- 
Seyler : 
Even though definite compounds of potassium with organic 
substances which might be considered essential to life-processes 
are unknown, the presence, without exception, of potassium in all 
organisms from the lowest to the highest compels us to assume that 
compounds of this metal play a necessary réle in all general devel- 
opmental processes. The organs of the invertebrates also always 
contain potassium, and those parts of plants contain the greatest 
amount of potassium which have the greatest developmental pow- 
ers. The power of organisms to separate from and retain the 
potassium of the liquids which nourish them is shown especially 
well by the fact that fresh-water streams and lakes and sea-water 
contain only very small amounts of potassium beside much larger 
amounts of sodium, calcium, and magnesium, yet organisms grow- 
ing in them contain much potassium, which they have been able to 
collect only from these waters which are so poor in potassium, and 
from nowhere else.” 
1This is not correct. The Serino water contains Ca which is also necessary for 
regeneration. [1903] 
2 Physiologische Chemie, p. 61. 
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