132 ANIMAL LIFE AND SOCIAL GROWTH 



or even of fresh water animals gave almost as 

 good results; even the culture medium in which 

 Paramecia had lived proved to be generally 

 effective. It is sufficient to record here that the 

 experiments showed that the conditioned water 

 does definitely protect the worms exposed in it 

 so that they live longer than if they were placed 

 directly into untreated fresh water. Just how 

 the animals conditioned the water to secure this 

 beneficial result is not known. It is known that 

 the protection furnished by these conditioned 

 solutions is about the same as that furnished by a 

 sugar solution that exerts an osmotic pressure of 

 about five atmospheres; yet the medium itself 

 exerts no osmotic pressure. 



The flatworms tested in America are called 

 Procerodes. They live near the low- tide regions 

 under stones which may be washed by fresh 

 water if heavy rains fall at times of ebb tides. 

 They live in small natural clusters although each 

 individual worm is distinctly separate. Such 

 clusters cover the stone's surface to an extent 

 equal to the size of a half-dollar or less. In the 

 laboratory they collect in great numbers about 

 the edges of stones where they come into contact 

 with the bottom of the aquarium. Whatever 

 other significance these aggregations possess, 

 they do have the possibility of giving their mem- 



