It is also interesting that many, perhaps most, patients with this condition also have skin allergies, eczema and/or asthma. The patient with moderate to severe icthyosis often has problems sweating due to the buildup of scales on the skin. The scales essentially seal the sweat glands.
For now, it is good to know the names. These names apply to all major and minor scales. 1  1st-Tonic. 2  2nd-Supertonic. 3  3rd-Mediant. 4  4th-Subdominant. 5  5th-Dominant. 6  6th-Submediant. 7  7th-Leading Tone.
Indeed, in a diatonic scale, there's only one d5, and this interval does not meet the strict definition of tritone, as it is formed by one semitone, two whole tones, and another semitone: d5 = s+t+t+s.