The second stage consists in the closure of the jaws. This com presses the nipple, which lies embedded in a groove of the tongue, and forces the milk into the mouth. The negative pressure induced by the act of sucking has been measured by Pfaundler. it is possible that a sum of successive sucks are produced, whereby the pressure may rise to 30 cm. (water or inilk in the manometer); in older and vigorous infants it may attain even a pressure of 70 cm.
The act of sucking is the only important function which may be assigned to the mouth organs of the nursling. All other mechanical functions, such as the amylolytic activity of the saliva and the detergent properties of the secretions, are superfluous for the infant nourished exclusively on milk. it is conclusive, therefore, that the mouth of the infant, as a special organ of digestion, holds a subordinate position, but rather assumes the role of an indifferent passage-way for the milk.
The inability to perform the act of sucking may obviou.sly endanger the life of the infant. As diseases of the mouth are very frequent ante cedants of the inability to nurse, the importance of a knowledge of its diseases and their treatment is clear; and, for reasons mentioned, even insignificant lesions require the attention of the physician.
The mucous membrane of the infant's mouth is tender, easily vulner able, and, consequently, the frequent scat of superficial lesions. In spite of a strong healing tendency, these minute defects serve, under certain conditions, as a nidus for a local bacterial invasion which by extension occasionally produces serious grades of disease and may even lead to sepsis. The most frequent source of injury to the mucous mem
brane is found in the manipulations performed in cleansing the mouth.
The so-called epithelial pearls are very singular anatomical structures of the gunis. On account of the frequency of their presence (over 90 per cent.) they must be regarded as a physiological appearance, al though they must be considered as minute retention-cysts of thC mucous glands. They arc filled with pavement epithelium. These anatomical peculiarities are often called 13ohn's nodules after the author who first described them. They are commonly situated in or beside the raphe, also in the upper posterior alveolar border and on the hard palate. They vary in size from a millet seed to a pinhead and present a shining milky or yellowish color. The nodules gradually disappear by spon taneous absorption or by ulceration and discharge of their contents.
The second dentition begins in the fifth or sixth year with the erup tion of the third molars. The deciduous teeth drop out approximately in the sante order in which they appeared. In the twelfth year the fourth molars and, lastly, in the sixteenth to twenty-fourth year the fifth molars, the so-called WiSdOM teeth, pierce the gums.