[9] In our tables of mortality we find teething registered as having occasioned the death of nearly 5 (4.8) per cent. of all children who died in London under one year old; and of 7.3 per cent. of those who died between the age of twelve months and three years. PART III. _ON THE DISORDERS AND DISEASES INCIDENT TO ALL PERIODS OF CHILDHOOD._ The ailments hitherto noticed are by no means all that may occur during infancy and early childhood, but those only which either happen then exclusively, or at least with far greater frequency than at other times. It will be most convenient to consider the others under the different systems to which they belong, as diseases of the head, of the chest, and of the bowels. Before entering on these new subjects, however, a few words may not be out of place with reference to what may be termed the second period of childhood. It is above all a time of wonderfully lessened sickness and mortality. We have not the means of stating exactly the rate at which mortality is lessened between the cessation of the first and the commencement of the second dentition; but we do know that it is ten times less between the age of one and five, and nearly twenty times less between five and ten than it was in the first year of existence.[10] A mother's anxiety then may safely be quieted after the first year of her infant's life, and still more after the first set of teeth have been cut, for if her child is strong and healthy then, there will be comparatively little to fear for its future. Four years or thereabouts now follow, before any important change takes place in the child's condition, for it is not until between six and seven years old that the first set of teeth begin to be shed, and the second to take their place. This change of teeth too is of far less moment as far as the health is concerned, than was the cutting of the first set. The first dentition was the preparation for an entirely new mode of life for the child, and was intended to fit it for a life independent of its mother. The second has no such signification; it is a mere local alteration rendered necessary by the growth of the jaws, and takes place quietly, by the gradual absorption of the roots of the first set of teeth, brought about by the pressure of the others as they approach the surface. Four teeth in each jaw are new, and replace no others, but usually they are cut without much discomfort, and the wisdom teeth do not concern us here, for they do not appear until childhood has long passed.