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 rv 



Amount of Salt Average Growth 



in the Solution in Nine Days 



5.1 0.5mm. 



4.8 - 4 



4.4 - 7 



4.1 - - 12 



3.8 (normal sea-water) - - 12.6 



3.2 - - 14.3 

 2.2 - 15 



1.9 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- 





