DEATH 405 



by Minot and others. Forms living in warm climates are not as 

 long-lived as those in colder regions because of the higher rate of 

 metabolism at the higher temperature. The human races of the 

 tropics are not as long-lived as the races in cooler regions. The 

 secret of long life is to " keep cool." 



7. Lepeschkin, Dhar, and others have concluded that the chief 

 factor in the death of cells is related to a denaturation of their 

 protoplasmic colloids. This denaturation, associated with co- 

 agulation, may be due to various causes, but the end result is 

 the same, viz., a failure of the cell to function normally, this de- 

 crease in normal function finally terminating in death. 



8. Along with metabolic theories must be included that of 

 Benedict, who associated death in plants with a decrease in per- 

 meability of the cells. This would result in the slowing up of the 

 elimination of toxins and other injurious metabolic products, 

 with their resultant accumulation in the cells. That such accumu- 

 lations occur is certain, and the plant sheds the portions con- 

 taining them when possible. 



The fact that local death may occur in plants without general 

 death is an accompaniment of the lack of complexity found in 

 plants. If a plant possessed a nervous and a vascular system 

 which connected all parts in the intimate way in which animal 

 tissues are connected by the nerves and the blood vessels, local 

 death would be impossible. Poisons formed in one place would 

 be carried to another, and the death of one portion would result 

 in the death of the entire organism. That such death does not 

 result when leaves, the bark, the wood, etc., die, is a result of 

 this inferior specialization, which thus has its advantages as well 

 as its disadvantages. 



9. Jennings (1912), Loeb (1919), and Pearl (1922) have con- 

 cluded that death is the result of differentiation without the 

 power to repair losses. As the germ and body cells have become 

 differentiated, the latter have lost their embryonic nature and 

 with it the power to repair all loss. They cannot remain juvenile 

 like the germ cells, but must become old and die. This explains 

 why plants with indefinite growth and several meristematic re- 

 gions, have an indefinite length of life. Similarly, in the bacteria 

 and Protozoa, the rejuvenated cells resulting from fission never 

 lose the power to repair losses and hence never become senile. 

 As Loeb states the case : 



