It is not necessary, in order to lead to the contraction of these muscles, that air should actually be expelled from the chest; it suffices that the muscles of the chest and abdomen should contract with great force, whilst by the closure of the glottis no air escapes. In violent vomiting or retching the diaphragm is made to descend by the chest being filled with air; it is then held in this position by the closure of the glottis, “as well as by the contraction of its own fibres.”[613] The abdominal muscles now contract strongly upon the stomach, its proper muscles likewise contracting, and the contents are thus ejected. During each effort of vomiting “the head becomes greatly congested, so that the features are red and swollen, and the large veins of the face and temples visibly dilated.” At the same time, as I know from observation, the muscles round the eyes are strongly contracted. This is likewise the case when the abdominal muscles act downwards with unusual force in expelling the contents of the intestinal canal. The greatest exertion of the muscles of the body, if those of the chest are not brought into strong action in expelling or compressing the air within the lungs, does not lead to the contraction of the muscles round the eyes. I have observed my sons using great force in gymnastic exercises, as in repeatedly raising their suspended bodies by their arms alone, and in lifting heavy weights from the ground, but there was hardly any trace of contraction in the muscles round the eyes.