Physiology of Regeneration 633 
The list of instances of the stimulating or the inhibiting effect 
of various reagents on different manifestations of life could be 
easily lengthened. From all these it may be safe to infer that 
similarity of the effects produced ‘by reagents on various functions 
of living organisms—be they growth, development or regenera- 
tion—implies a general cause, which is to be found in the aug- 
mentation or depression of the protoplasmic activity of the indi- 
vidual cells of these organisms, which is really the only source of 
energy for all functions. 
VII CONCENTRATION AND DILUTION OF SEA-WATER AS A FACTOR 
IN THE RATE OF REGENERATION 
Loeb (’92) found that upon bringing stems of hydroids into 
sea-water of various degrees of concentration the number of regen- 
erating hydranths is either increased or decreased depending upon 
the concentration, the optimum, however, being sea-water diluted 
to about 66 per cent. Similar results were obtained since then 
by Snyder, Peebles and some other investigators. This interest- 
ing fact, of what is supposed to be the effect of osmotic pressure 
upon regenerating animals, calls for some more experiments for 
its final establishment. I therefore devised a number of experi- 
ments with the purpose in mind of further studying this phenome- 
non. In 1907 my material unfortunately ran short, so that only 
three experiments were performed. Briefly stated, the experi- 
ments and the results were as follows: Two solutions of sea-water 
were used; in one case the sea-water was diluted with an equal 
volume of distilled water, in the other with one-third its volume 
of distilled water, giving respectively a 50 per cent and 75 pet 
cent mixture. The 50 per cent mixture was very injurious to 
the worms, and though some of them lived for quite a long time, 
none had proliferated any new tissue. The 75 per cent mixture 
acted less injuriously, but even it produced a marked retarding 
influence upon the rate of regeneration. The concentration of 
the sea-water was brought about by the addition of 2 per cent 
of MgCl, to the sea-water. In this case also the animals suffered 
a considerable reduction in the power of regeneration. 
