Another class of consonants are the so-called sonants or liquids, _l_, _m_, _n_, and _ng_. In these the vocal tone may have appreciable duration; we can hum a tune on any one of them; _m_, _n_, and _ng_ are emitted solely through the nostrils, the orifice of the mouth being completely closed. _R_ may be pronounced in two ways, the trilled or rolled _r_ being best for the purposes of singing. Another form of this consonant, made by the vibration of the uvula in contact with the back of the tongue, is essential to a correct (conversational) pronunciation of both French and German, although it has no place in English. The rolled _r_, however, is generally used in singing by both the French and the Germans. IV A highly beneficial form of physical exercise is found in the regular daily practice of singing. All the muscles of the abdomen and thorax are strengthened by this exercise; the lungs are developed to their greatest normal capacity, and the habit is formed of breathing at all times in the most healthful manner. Both the circulation and the digestion share in the benefits derived from regular vocal practice, and the general health inevitably reflects the advantages incident to a proper performance of these most important bodily functions. An erect and graceful bearing, with well poised head and shoulders and firm, elastic step, can be secured through the correct practice of singing more readily than in almost any other way. Yet the professional use of the voice imposes considerable restrictions on the singer’s habits of daily life. As Sir Morell Mackenzie has said, the singer is an athlete who must always be in training. A perfect condition of the voice demands a perfect state of general health. The singer must plan his whole life in conformity with the demands imposed on him by his art. The slightest indisposition of any kind is almost invariably reflected in the voice. Under the conditions in which people in the usual walks of life are placed, slight colds and trifling upset states of the digestive organs are a matter of almost no concern. But with the professional singer conditions are entirely different. So delicate and finely adjusted are the laryngeal muscles of the cultivated voice that their ‘tone’ may be upset by apparently insignificant causes. The mucous membranes of the larynx and throat are also highly sensitive to severe and unfavorable conditions.