[26] A further aid to the circulation in the naso-pharynx is afforded by the lusty use of the voice. It a natural for the young human to cry and to shout, and unless this instinct is allowed full play the child is apt to suffer in health. I cannot but think that the modern child is too much repressed in this respect, and that he is not afforded, especially in towns, proper opportunity of venting his vocal energy in out-door play. May we not have here a contributory factor in the causation of adenoids? [27] Among the Australian skulls I have examined in museums caries of the wisdom teeth--_i.e._, in those very teeth which, as shown by their atrophy, are least used--is by no means uncommon (though it is possible that some of the skulls belong to natives who have embraced the dietetic customs of the white man). I submit that this fact may fairly be used as an argument in favour of the view that inefficient use of the teeth predisposes them to caries by interfering with their resisting power, though it must be acknowledged that the position of the wisdom teeth places them at a disadvantage, owing to the tendency of food to accumulate about them, especially in undeveloped jaws in which they have not adequate room. [28] This film can be felt by the tongue as a somewhat rough covering, which gives place to a smooth surface after the use of the tooth-brush. [29] By the term “external stimulus” I mean here without distinction every outward agency of nature, as well as every agency which has its seat within the organism. The word “external” applies here to everything with the single exception of the nervous system itself. [30] One may be permitted to use this expression for the sake of brevity. [31] _Kwas_ is a favourite Russian drink, prepared from water, bread or meal, with malt and yeast. It contains a considerable quantity of lactic acid, some acetic acid, and other products of fermentation. [32] An investigation by Cannon and Day (_American Journal of Physiology_, 1903) has confirmed this conclusion. An hour after starchy food mixed with saliva was ingested a unit volume of the food in the cardiac end of the stomach contained almost twice the amount of sugar found in a unit volume of the food in the pyloric end. [33] The results of this investigation were reported to the Boston Society of Medical Sciences, November 19, 1901. [34] Without the possibility of seeing the relations of a movement to the ends of the intestine, it cannot be stated absolutely whether the movement is peristaltic or antiperistaltic. Such relations can be seen on the fluorescent screen only near the stomach and near the ileocæcal valve. The evidence that advancing peristalsis is the normal movement is so overwhelming that I have assumed that when food is moving in loops not visibly related to fixed points it is moving forward. [35] In this case the fæces were soft.