HUMAN LONGEVITY. 135 



admitted, does not enable us to exclude altogether those 

 noxious ingredients (some of them doubtless animal or 

 vegetable organisms) which produce epidemic and endemic 

 diseases. Nor can we yet deal with those equally unknown 

 influences on the body, for good or for ill, which depend on 

 electrical states of atmosphere, the proportion of ozone, &c. 

 But science is now actively directed to these various objects ; 

 and meanwhile we may fairly assume change and freedom of 

 air by ventilation to be the most efficient preventive means in 

 our power. 



Looking next to aliment in its connection with health, and 

 therefore with longevity, we encounter a topic which has 

 been endlessly discussed and written upon, and made the 

 subject of various and conflicting opinions. All this is 

 natural and inevitable. For the subject in question em- 

 braces not only what is necessary to human existence, but 

 also what belongs to man's luxury and sensuality; and is, 

 moreover, connected with all those changes of bodily con- 

 dition, whether healthy or morbid in kind, which are most 

 open to common observation. Including further those many 

 forms of liquid, from simple water to the strongest alcoholic 

 drinks, which the natural or perverted ingenuity of man has 

 mingled with his aliment, it brings in another class of effects, 

 of deep interest not only to individuals but to the welfare 

 of social life. 



Vague though it may seem, we can find no more fitting 

 word than moderation, to express that which is best in diet 

 in relation to health and length of life. No specification of 

 the wholesome or unwholesome in food can be of avail for 

 good, unless submitted to this one condition. As in the 

 relation of the lungs to air, so the digestive organs require a 

 certain quantity of food varying in different individuals, 

 and in the same person, at different periods to maintain the 

 healthy state and sufficiency of the blood, and through this 



