INTERACTION OF ORGANISMS 7 



rest fundamentally on the power of all protoplasm to 

 respond to certain outside influences and to execute 

 forcible movements by the utilization of energy liberated 

 from food. The nervous system and the brain itself are 

 likewise to be included in this mechanism of adjustment 

 of the body to its surroundings and of its various parts 

 to one another. 



5. The Interaction of Organisms on one another is 

 likewise a most important subject. Every plant and 

 animal is more or less influenced by its neighbors, but in 

 some cases the association is so close that both benefit 

 from it, or one benefits at the expense of the other. The 

 former constitutes the relation of symbiosis (from the 

 Greek sym- with, and bios- life) and the latter that of 

 parasitism. The first is less common and of slighter im- 

 portance. The latter relation very commonly gives rise 

 to a condition of disease in one of the parties to the asso- 

 ciation. This is of enormous importance in both plants 

 and animals. Every year millions of dollars worth of 

 crops are lost through the attacks of parasites. The loss 

 and suffering due to the action of parasitic bacteria on 

 animals — including man — is too familiar to need more 

 than bare mention. 



6. Death comes to all highly organized living beings 

 sooner or later. Each begins as a single small bit of liv- 

 ing matter (a cell) which by repeated divisions and 

 specialization finally grows into the mature individual. 

 This may live but a few hours or it may live thirty cen- 

 turies, but in the end it reaches its span of life. Of 

 course most organisms meet death in nature from vio- 

 lence — injury or disease — but nevertheless it has not 

 been possible so far for the biologist to prolong life in- 

 definitely in any highly organized type. It is in conse- 

 quence a very interesting and important problem to 

 ascertain just what are the conditions which determine 

 that protoplasm is alive one moment and dead the next. 



7. The Decomposition of Organic Remains is one 



