86 SYSTEMS OF TREATING STAMMERING of the voice is brought about by an increase or decrease in the tension of the vocal cords, this increase or decrease in tension being effected through muscular action. The voice is given the characteristic quality of different vowels through changes in shape of the buccal cavity, these changes being effected by alterations in the position of the lips and alterations in the shape and position of the tongue. The consonants are formed by different obstructions presented to the vocalized or non-vocal- ized expiratory current.1 This elucidation of the general physiological pro- cesses of speech is followed by detailed instruction concerning the manner in which the individual con- sonants are produced. The stammerer then pro- duces them himself, and afterward practises them for months or years, as the case may be, with the dif- ferent articulatory exercises. Needless to say, he is counselled to form the consonants at all times accord- ing to directions. The directions are typically as follows: To produce the consonant £, press the lips firmly together, raise the velum in order to separate the nasal cavity from the pharynx, and compress the air in the buccal cavity by the action of the respiratory muscles; now separate the lips (by the action of the labial muscles and the downward movement of the lower jaw), and the consonant is formed by the emission of the breath under pressure. To form by proceed as above, but vocalize the breath a moment before disploding the consonant. 1A detailed exposition on the physiology of speech can, of course, be found in almost any good book on phonetics or elocution.