Physiological Mobphology 97 



osmotic changes are the sources for the energy which is needed 

 to overcome the resistance to growth.^ 



In order to ascertain whether I could determine what are 

 the mechanical causes of growth in animals, I began at Naples 

 some experiments on Tubularia mesembryanthemum. I chose 

 long stems belonging to the same colony and distributed them 

 in a series of dishes containing sea-water of different concentra- 

 tions. In some of the dishes the concentration had been raised 

 by adding sodium chloride, and in others it had been lowered by 

 adding distilled water. According to the laws of osmosis the 

 amount of water absorbed by the cells of these Tubularians 

 differed with the concentration of the sea-water, the amount 

 being greatest in the most diluted solution and least in the most 

 concentrated solution. If now in reality the mechanics of 

 growth is the same for animals as for plants, we should expect 

 that the more diluted the sea-water the more rapid would be the 

 growth in the Tubularian stem. Of course, finally, a limit is 

 reached where the water begins to have a poisonous effect. It 

 was found, indeed, that within certain limits of concentration 

 the increase in the length of the stems during the same period 

 was greatest in the most diluted and least in the most concen- 

 trated sea-water. It is remarkable that the maximum of growth 

 took place not in sea-water of normal concentration, but in 

 more diluted sea-water, though this of course may not be the 

 case in all animals. The following curve (Fig. 33) will give an 

 idea of the dependence of growth upon the concentration of 

 the sea-water in Tubularia. The values for the amount of 

 sodium chloride, in 100 cubic centimeters of sea-water, are 

 represented on the axis of the abscissa, the values for the 

 increase in growth on the axis of ordinates. 



These and similar experiments, which for lack of space 

 cannot be mentioned here, show that growth in animals is 



1 The substance which is formed and which causes the swelling may be an 

 acid. I found that acids cause a swelling of muscles and it has since been shown 

 that this is a general phenomenon. 



