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222 indefinitely—challenge our earnest attention and demand our careful consideration. Let us first inquire what are the diseases which are the immediate cause of the great bulk of infant mortality. These may be grouped in four main classes, namely:

(1) The acute infectious zymotics, of which the chief are measles, scarlet fever, small-pox, diphtheria, and whooping-cough. These are collectively responsible for from fifteen to twenty per cent of the deaths under five.

(2) The acute lung-diseases, chiefly bronchitis and pneumonia, which together cause from ten to fifteen per cent of the deaths under five. In America, more than twice as many deaths occur from pneumonia as from bronchitis, while in England nearly the reverse is true.

(3) Tubercular and constitutional diseases, such as consumption, scrofula, meningitis, and hydrocephalus, which are responsible for from ten to fifteen per cent of the entire infant mortality.

(4) The diarrhœal diseases, comprising infantile diarrhœa, cholera infantum, inflammation of the bowels, dysentery, and some others. These are the cause of at least one fourth of the entire infant mortality the world over; while in America cholera infantum alone is responsible for nearly or quite one fifth.

But the problem before us is not one which can be solved by a simple rehearsal of the names of diseases and the number of their victims. These only show the form and manner of death, while the ultimate causes lie far in the background.

The real questions at issue relate to those influences which are at work upon so large a proportion of infants and young children the world over, tending to break down in them the power of resisting disease, lessen their chances of a vigorous, healthy life, and render them unduly liable to go down to early graves. What is the nature of these influences? What circumstances tend to increase their activity? Under what conditions and to what extent may they be rendered inert, or their usual dire effects be avoided? By what means may an unfavorable environment be changed to a favorable one, and the vitality and longevity of the race be thereby increased?

In considering these questions, it must be remembered that the causes of infant mortality are also the causes of adult mortality, only in a less degree; and that the health of a delicate infant is the most sensitive measure which we possess of those influences which are deleterious to health, either in infancy or adult life.

The first of these deleterious influences in the order of time, and unquestionably also of importance, is heredity. A very large proportion of all children born into the world are either weaklings or invalids from the beginning. They are born wrong. They come from poor stock. The influences which determine their weakness