All the normal rhythms are physiologic, are the expression of organic activity, but there are many which are gross exaggerations in their intensity, and some unphysiologic in their morbid expression; but rhythms, diurnal, weekly or monthly, which demonstrate an alteration in either the psychic or physiologic conditions, and as such, must be studied and utilized when treating psychic or functional disturbances.
Every living cell, and the multifarious resultant products and ultimate complete organizations due to the activity of cells are controlled, governed and developed through rhythmic action. Sunlight and darkness, the ebb and flow of tides, the regularity of the seasons, the periods of growth and decline, activity and rest, fecundation and sterility, exaltation and depression, nutrition and decay have a law of regularity and alteration fixed and immutable. These coarser variations in the rhythms which are a part of our environment are duly acknowledged, and our habits adapted accordingly.
HOWARD WL. PHYSIOLOGIC RHYTHMS.THE PRACTICAL VALUE OF THEIR RECOGNITION IN TREATMENT OF FUNCTIONAL NEUROSES.. JAMA. 1899;XXXII(20):1089-1091. doi:10.1001/jama.1899.92450470011001d