INTRODUCTION 13 



1. Heredity: always influential and sometimes definite- 

 ly and hopelessly limiting the life span. 



2. Infection: acute or chronic, by bacteria or para- 

 sites — probably the most potent cause of disease, old 

 age, and death. 



3. Poison: from within or without; drugs, occupational 

 poisoning, endocrine (glandular), or other disturbances 

 releasing poisons or interfering with their elimination or 

 destruction; protein sensitization. 



4. Food deficiency: general, as in a lack of sufficient 

 food; or specific, as in a lack of some particular food 

 substance — mineral, vitamin, amino acid, regulating 

 food, and so forth. 



5. Food excess : general, as in overeating ; or specific, as 

 in excessive consumption of meat, sugar, or starches. 



6. Hormone deficiency: as in endocrine, or other or- 

 ganic deficiencies. Hormone deficiency is probably the 

 greatest immediate factor in limiting the life cycle. It 

 implies a lack of some substance or group of substances 

 whose function is to stabilize the tissues in a state of 

 health. 



7. Hormone excess : as in the opposite state of endocrine 

 overactivity. 



8. Physical trauma: an obvious factor in life destruc- 

 tion, yet even physical overwork is not so often the cause 

 of organic strain or injury as was formerly thought. The 

 yielding organ is probably already damaged by infection 

 or poison. 



