224 STUDIES IN GENERAL PHYSIOLOGY 
went no farther. I now divided the concentrated sea-water 
and the animals contained in it between two vessels, and 
added enough distilled water to one of them to restore it to 
the concentration of normal sea-water. After a few days 
all the animals in this vessel regenerated their polyps in an 
entirely normal manner, but no regeneration whatsoever 
occurred in the other. I have repeated this experiment sey- 
eral times, always with the same result. While, therefore, 
a great lowering of the concentration of the sea-water (334 
per cent.) not only does not inhibit regeneration, but may 
accelerate it, an increase in the concentration to a like 
amount suffices to prevent regeneration altogether, or almost 
entirely, without, however, injuring the power of regenera- 
tion, provided the animal does not remain too long in the 
concentrated solution. 
3. In order to determine the limit of concentration in 
which regeneration is possible, I evaporated normal sea-water 
to 90, 80, 75, 70, 60, and 50 per cent. of its volume. The 
solutions were filtered and shaken for some time in the air. 
Regeneration took place in the first three solutions, but not 
in the last three. Regeneration, however, did not occur 
simultaneously in the first three solutions, but the more 
slowly, the more concentrated the solution. After lying for 
several days in the 70 per cent. solution, the Tubulariz had 
not lost their power of regeneration, but in the stronger 
solutions even this had suffered. When the Tubularians 
were brought back from the stronger solutions into normal 
sea-water, they no longer formed polyps. The tissues of 
the stem were shrunken and often separated from the peri- 
derm. Upon the other hand, when I added as much as 50 
per cent. of distilled water to ordinary sea-water, a distinct 
inhibition of the process of regeneration could not once be 
noted; only upon the addition of 100 per cent. of distilled 
water did regeneration cease. If still more distilled water, 
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