340 GENERAL PHYSIOLOGY 



among insects. While in man adult life is extremely long in 

 comparison with that of the embryo, in most insects the reverse 

 prevails. Many insects die very soon after copulating or deposit- 

 ing the eggs ; the only individuals to live longer are those that do 

 not copulate. The best example is afforded by the day-flies. The 

 completely-developed adult individuals frequently live but a few 

 hours, dying immediately after depositing the eggs. These facts 

 prove most strikingly that the causes of death are not to be found 

 in the summation of many external injuries, but are already 

 established within the organism itself, and death is simply the 

 natural end of development. In other words, the problems of 

 development and death belong inseparably together, the latter is 

 merely a part of the former. 



We will now summarise the results of these considerations once 

 more and in somewhat different words. The idea expressed 

 regarding the causes of natural death is based upon the impor- 

 tant fact that the organism undergoes uninterrupted change 

 from its individual origin to its death. The various parts of the 

 organism, however, take part in this change in very different 

 degrees and at very different rates. In this manner there comes 

 gradually in the life of every organism a time when the action of 

 its mechanism has experienced such a disturbance through the 

 changes that the individual parts have undergone in its develop- 

 ment, that it passes into death. For the multicellular organism 

 this means that from internal causes the various cells and cell- 

 groups of its organs become gradually so changed in their de- 

 velopment, that with the close dependent relation among all cells, 

 tissues, and organs, the disturbance of their co-operation becomes 

 constantly greater until the organism dies. The immediate causes 

 of death may be very different for the different cells of the multi- 

 cellular organism. Many of the cells and tissues invariably die 

 from causes lying outside of them but within the organism, 

 because the parts upon which they are dependent, which belong 

 to their external conditions of life, as, e.g., the nerve-centres, have 

 undergone disturbances and have died. If the ganglion-cells 

 whose activity controls the movements of respiration have perished, 

 respiration ceases, the heart stands still, blood circulates in the tissues 

 no longer, the tissue-cells are no longer nourished, and all the 

 tissues alike perish sooner or later, because their external con- 

 ditions of life are withdrawn. But, if the individual tissue-cell 

 does not die from external causes, exactly the same is true of it 

 as of the cell-community the condition of its living substance 

 undergoes uninterrupted change from internal causes, and there 

 gradually develops a point of time when the disturbances in the 

 co-operation of its constituents have become so great that life 

 ceases. These statements do not, indeed, disclose the special 

 events in living substance, the result of which is death, no more 



