234 STUDIES IN GENERAL PHYSIOLOGY 
concentration of the solution in which they are contained 
does not exceed a certain limit; this limit is attained when 
1.6 g. of NaCl is added to 100 c.c. of sea-water—when the 
solution contains 5.4 per cent. salt. As the concentration 
decreases, the Tubularian stem must absorb more and more 
water from the solution, and we therefore find linear growth 
to increase with a decrease in the amount of salt in the solu- 
tion, until the limit is reached where the poisonous effects 
of the large amount of water show themselves. From this 
point on a further increase in the amount of water contained 
in the animal must cause growth to fall rapidly to zero. 
This accounts for the rapid fall in the curve between the 
values 1.9 and 2.5 of the abscissa. 
A second experiment, performed under entirely similar 
conditions, yielded the same result as the above. This 
is shown by Table IV. 
TABLE IV 
Amount of Salt Average Growth 
in the Solution in Nine Days 
51% - - - - - 0.5mm. 
4.8 - - - - 4 
44 - - - - 7 
4.1 - - - 12 
3.8 (normal sea-water) - - 12.6 
3.2 - 14.3 
2.2 - - - 15 
19 10.5 
As in the preceding experiment, linear growth increases 
in this case also with a decrease in the concentration, attain- 
ing a maximum, not in ordinary sea-water but in a more 
dilute salt solution about 2.2 per cent. Beyond this point 
growth falls rapidly. In other experiments also—which, 
however, I omit here because I failed to measure the in- 
crease in the length of all the specimens, and therefore cannot 
tabulate them—I was able to show that the relation be- 
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