Anything that makes for good may be rendered harmful in its effect by injudicious application or improper use, and many authorities have referred to this fact in connexion with breathing exercises. For the guidance of my readers I will detail some of the harmful results which accrue from the attempt to take what are known as “deep breaths” during the practice of breathing and physical exercises, in accordance with the instructions set down and the principle advocated in recognised breathing systems. At the outset, let me point out that respiratory education or respiratory re-education will not prove successful unless the mind of the pupil is thoroughly imbued with the true principles which apply to atmospheric pressure, the equilibrium of the body, the centre of gravity, and to positions of mechanical advantage where the alternate expansions and contractions of the thorax are concerned. In other words, _it is essential to have a proper mental attitude towards respiratory education or re-education, and the specific acts which constitute the exercises embodied_ in it, together with a proper knowledge and practical employment of the _true primary movement_ in each and every act. I may remark that I recognised this factor and put it to practical use over twenty years ago, but it has been quite overlooked or neglected in the other systems formulated before and since that time. In fact, when I introduced my method to leading London medical men they quickly admitted the value of this important factor, and expressed their surprise that on account of its importance it had not been previously advocated, seeing that from a practical point of view it is so essential, not only in the eradication of respiratory faults or defects (re-education), but also in preventing them (education). A proper mental attitude, let me repeat then, is all-important. From its neglect arise many of the serious defects ordinarily met with in the respiratory mechanism of civilised people, all of which are exaggerated in the practice of customary “breathing exercises.” 1. “_Sniffing_” or “_Gasping_.” If the “deep breath” be taken through the nasal passages there will be a loud “sniffing” sound and collapse of the alæ nasi, and if through the mouth, a “gasping” sound. The pupil has not been told that if the thorax is expanded correctly the lungs will at once be filled with air by atmospheric pressure, exactly as a pair of bellows is filled when the handles are pulled apart. It is a well-known fact, but one greatly to be regretted, that many teachers of breathing and physical exercises actually tell the pupils that, in order to get the increased air-supply they _must_ “sniff.”