nose, not through the mouth
Breathing exercises should be deep, slow, rhythmic, and through the
nose, not through the mouth. A certain Oriental deep-breathing exercise
is particularly valuable to insure slowness and evenness of the breath.
It consists of pressing a finger on the side of the nose, so as to
close one nostril, breathing in through the other nostril, breathing out
of the first nostril in the same manner and then reversing the process.
Attention to the slight sound of the air, as it passes through the nose,
enables one to know whether the breathing is regular or is slightly
irregular. Such breathing exercises can be taken at the rate of three
breaths per minute, and the rate gradually reduced until it is only two
or even less per minute.