In the minds of many intelligent and thoughtful physicians there is, no doubt, a feeling of unformulated distrust as to the real possibilities or probabilities of improving the health and diminishing the mortality of the community at large; and this feeling is in part due to the exaggerated claims and emotional exhortations of some advocates of hygiene. A careful and unprejudiced survey of what has been accomplished by sanitary measures will, however, largely dissipate this distrust. The natural term of the life of man is fixed by the physiologist at about one hundred years, which is nearly in accordance with the law indicated by Flourens, that the period of life of an animal is about five times that required to perfect the development of its skeleton and unite the epiphyses with the shafts of the long bones. The actual average duration of human life is less than half this, but there is satisfactory evidence that it has increased in civilized countries. The ancient estimate is expressed in David's declaration, that "the days of a man are threescore years and ten, and if by reason of strength they be fourscore years, yet is their strength labor and sorrow." Kolb, a cautious and learned statistician, concluded, from his studies, that while the maximum age reached by man has not materially changed for many centuries, the number of persons who now survive infancy and of those who reach a ripe old age has decidedly increased; and this opinion is sustained by Mr. Lewis, the secretary of the Chamber of Life Insurance of New York, who points out that while civilization largely interferes with the laws of evolution by survivorship, it aids by economizing the waste which occurs in its absence. "Under natural selection, when variations in capacity arise, thousands of them are wasted where one is secured, fixed, and transmitted. But human society economizes much of this waste, fastens upon and improves an immensely larger proportion of the capacities lavishly produced by Nature, and thus concentrates forces which would otherwise spread their operation over countless ages."[1] [Footnote 1: "Influence of Civilization on the Duration of Life," _Reports Am. Pub. Health Ass'n_, N.Y., 1877, vol. iii. p. 173.] We have, however, no record of the duration of life in ancient Greece and Rome, and it is quite possible that it was greater than in Western Europe during the Middle Ages, which formed a period of retrogression in a sanitary point of view. The Jew, the Greek, and the Roman, prior to the Christian era, were probably cleaner in person and in dwellings than the people of the time when dirt became the odor of sanctity. In the absence of reliable data for this country, it is impossible to speak with certainty of the results of attempts made here to prevent disease and death. Each sex, race, and age has its own rate of mortality, {175} and until this rate is determined we can only guess as to whether good work is being done or not.