THE MANIFESTATIONS OF LIFE 



49 



Sitotropic reactions, however, are observed among 

 lowly motile plants, such as bacteria. Thus Hertwig 

 has found that a 1 per cent, solution of beef-extract or of 

 asparagin has a pronounced attractive effect upon 

 Bacterium termo, Spirillum undula and numerous other 

 organisms. If a fine capillary tube filled with such a solu- 

 tion be held in contact with a drop of water containing 

 such organisms, a considerable mass of them will be 

 found plugging the mouth of the tube in from two to 

 five minutes, showing their movement from the poorer 

 to the richer nutrient supply in response to sitotropic 

 influences. 



Fia. 7. Amoeba ingesting a Englena cyst. 1, 2, 3, 4, Successive stages in the 

 process. (Jennings.) 



The amoeba gliding about takes up onj after another 

 objects suitable for food, as they come within its reach. 

 If few such be found, its movements become more ac- 

 tive and its excursions longer. 



A hydra with tentacles spread awaits the arrival of 

 its prey. If none come, it changes its position and tries 

 again. 



Caterpillars hatched upon the trunk of a tree climb to 

 the branches and reach the leaves upon which they feed. 



As we ascend the scale of life, and the behavior of the 

 organism becomes more and more complicated, the sito- 

 tropic, hydrotropic, and oxytropic reactions become so 



