Though all the exercises thus far referred to tend to develop the diaphragm and abdominal muscles, these may be strengthened by special exercises. The diaphragm is the soft floor of the chest, and must at once bear the strain of the air that acts on the approximated vocal bands, and assist in applying that pressure with just the amount of force required, and no more; hence it is important that this muscle be both strong and under perfect control. This large central muscle is probably not only the most generally effective of all the respiratory muscles, but has an action more precise and often more delicate, more nicely controlled, than that of any other. It is possible to make very powerful movements of this muscle, and an exercise that will cause it to descend deeply and remain in a tense condition is valuable. To effect this, one pushes it down as far as possible, and holds it there for a few seconds, then permits it to relax gradually. The extent to which this is successful can be inferred from the degree to which the abdominal wall bulges forward. The sudden though slight movements required in those forms of vocalization that bear more or less resemblance to what vocalists term _staccato_, and which are so effective in dramatic speaking and singing, can be prepared for by larger but sudden movements of the diaphragm, as when one taking a full breath imitates coughing movements, but in a regular and measured way, the throat being used but little. At the same time, or separately, the abdominal muscles may be effectively exercised by being drawn in and thrust out with considerable force. None of these movements are elegant--they scarcely put one in an artistic light; but they are highly effective in strengthening parts every voice-user must employ. To furnish adequate support for the diaphragm and chest in a very vigorous use of the voice, as in the most trying passages a tragic actor has to speak or a vocalist to sing, the abdominal muscles must remain more or less tense, and to do so effectually they must have strength beyond that possessed by the corresponding muscles in ordinary persons; hence the desirability of employing special exercises to increase their vigor. Hill climbing and bicycling also tend to this end, but the latter is for many reasons not a form of exercise to be recommended to one who wishes to attain the highest results with the voice. Wind, dust, a stooping position, excessive heat of the body, etc., are all among the many factors of risk for the delicate vocal mechanism. As the expiratory blast is so important in voice-production, the exercises above recommended should be followed by others in which this principle is specially recognized. 1. Inspire so as to fill the chest to the fullest with considerable rapidity; then allow the breath-stream to pass out with the utmost slowness.