134 GENERAL PHYSIOLOGY 



blood-current but also wander about actively in all the tissues of 

 the body and play an important rdle in the organic hoixsehold, re- 

 main in great part living, and, if kept under favourable conditions, 

 can live still longer. 



What moment then shall be designated as the moment of death ? 

 If the existence of vital phenomena be employed as the criterion, 

 then the moment when spontaneous muscular movement, espe- 

 cially the activity of the heart, ceases, cannot consistently be 

 regarded as the moment of death, for other cell-complexes con- 

 tinue to live for a long time thereafter. We see, therefore, that 

 there is no definite point of time at which life ceases and death 

 begins ; but there is a gradual passage from normal life to complete 

 death which frequently begins to be noticeable during the course 

 of a disease. Death is developed out of life. 



The history of death is very different in the different classes of 

 animals. In the warm-blooded animals death develops relatively 

 rapidly after the standstill of the blood-circulation, as a result of 

 the great dependence of all tissue-cells upon nourishment from 

 the blood-current. The cold-blooded organism passes from life to 

 death as a rule much more slowly ; the definitive death, i.e., the 

 state in which no further vital phenomenon can be perceived in 

 the body, appears in many cases only months after the animal has 

 experienced an irreparable, fatal injury. In harmony with the 

 greater independence of the individual organs in respect to the 

 blood-circulation and one another, in many cold-blooded animals 

 individual parts also, when severed from the rest of the body, can 

 survive for a long time, — a peculiarity upon which depends the 

 special usefulness of such animals, e.g., frogs, for many physio- 

 logical investigations. It is well known that a muscle with its nerve 

 can be removed from a frog's body, and under projaer conditions 

 can be maintained for experimentation alive and in an irritable 

 condition for days. The fact appears here much more clearly 

 than in the case of man, that death is not a condition that is 

 established in a moment, but is developed very gradually. 



It may be said that in all the cases mentioned multi- 

 cellular animals are under consideration, and in them one kind of 

 cell suffers death earlier, the others later ; but how is it with the 

 single cell, which in itself represents a living organism ? The 

 history of cell-death corresponds exactl}- with the development of 

 death in the multicellular organism, except that in the former the 

 various important points appear much more clearly. We see here 

 also that death does not occur suddenly, but that normal life is 

 united with definitive death by a long series of transition-stages, 

 following one another uninterruptedly, and frequently extending 

 through several days or, not rarely, several weeks. We have 

 already become abundantly acquainted with the fact that non- 

 nucleated protoplasmic masses that have been cut off from a cell 

 do not continue living. If such a separated piece of protoplasm. 



