HYDRA FUSCA 153 



tions, long after the frog itself has been killed. More remarkable 

 is this power in the case of a turtle, for here even when the animal 

 has its head entirely cut from the body, and the rest of 

 the animal destroyed, the heart, if removed and kept under 

 proper conditions, will keep on beating for at least two days. 

 Still more remarkable is it to find that in the air passages of the 

 turtle there are ciliated cells which have a special power of motion ; 

 Fig. 14 C. During all the life of the turtle these cilia are in a 

 state of active motion, and after the turtle is dead the cilia 

 may continue moving for as long as two weeks. We thus see 

 that among the higher organisms the death of the animal as a 

 whole does not necessarily involve an immediate death of all its 

 parts. The individual parts are, of course, closely dependent 

 upon each other, and, at least in the higher organisms, the life 

 of neither is capable of being long maintained without the other; 

 but the life of the individual cell may frequently continue some 

 time after the life of the organism as a whole has been brought 

 to an end. 



From this it follows that the term death may have a different 

 meaning in different connections. In speaking of the death of an 

 animal, we may refer, and usually do refer, to the death of the 

 animal as a whole, which means the destruction of the compli- 

 cated mechanism that forms the animal organism. But we may 

 also refer to the death of the individual parts, and in this case 

 the exact time when the animal comes to its death is difficult 

 to state. The animal as a whole may die on one day, while 

 some of its parts may remain alive at least two weeks. In 

 such instances it is not easy to say when death occurs. Never- 

 theless, it is customary to refer by this term, not to the death 

 of the individual parts or the individual cells which make 

 up the animal, but to the destruction of the organism as a 

 whole, which causes it to cease to act as a unit. Usually, 

 therefore, death refers to the breaking down of the mecha- 

 nism of which an organism is composed so that its parts do 

 not act together. 



