The second long-term rhythm, this one of 98-day duration, was ascribed by Fliess to the rhythmical changes of the feminine inheritance. Originating in the nervous system or fibers, it influences the emotions and one's degree of sensitivity. Fliess, a thorough researcher, explained his theories with firm conviction and documented them with an impressive collection of statistical data, tracing the origin of the rhythms back to birth. His revelations, to say the least, caused a good deal of Controversy among his colleagues. They accepted the fact that man's physical makeup and his emotions are continually changing; but it was, understandably, difficult for them to take the next step and agree that these changes were influenced not only by what man experienced in his everyday living, but quite fundamentally by his very biological constitution. To Fliess, it seemed as if nature had given man a master clock in addition to the more obvious rhythms that pulse throughout the animal and plant kingdom. There are, of course, innumerable examples of precise rhythms in all forms of life, from the simplest virus to the most complicated creatures.

In a book published in 1942, George Riebold, a gynecologist, reviewed the fundamental ideas developed by Fliess between 1908 and 1928. Riebold said that "some truth lurks in the idea that life follows a periodic rhythm . . . and that the periods of 23 days and 28 days which Fliess discovered are of frequent occurrence." Some of the discoveries, he reported, had been adopted into modern concepts of gynecology and otolaryngology.

The word rhythm is also used in reference to the menstrual cycle in woman, for which a 28-day periodicity is the apparent average. Two questions were foremost in the mind of the original researchers: First, why does this supposedly regular menstrual rhythm vary in length in different women (and even in the same woman) from about 26 to 35 days? Secondly, why should woman alone be subject to rhythmical development? Is not man also, the researchers reasoned, the combination and offspring of both male and female cell development? After Fliess had reported on bisexuality in man, he observed a 23-day rhythmical repetition in fevers and recurrent illness in some of his patients. This led him to believe that both a 23-day and 28-day rhythm affected the regularity of the menstrual rhythm and that all life is influenced by these two long-term rhythms. ...There is a lesson to be learned from the lifetime efforts of the pioneers in biorhythm, Swoboda and Fliess. It is included in these pages because it is important to an understanding of the history of biorhythm, or, for that matter, of just about any new idea that stretches the imagination of man beyond his common experience. Fliess was primarily a researcher in the field of life rhythms. In their questioning however, both Swoboda and Fliess felt that the problem of rhythms in nature could best be solved by examining as many facets of her manifestations as possible. Independently, both studied family trees, hoping to find out why births often followed a rhythmic family pattern. Curiosity led them to attempt to establish a biological pattern between siblings, and between the child and his parents and grandparents....

Their awe of nature led these pioneers to experiment with numbers as a tool in deciphering her wondrous accomplishments. The irony of their quest was that this very use of mathematics helped largely to defeat their attempts to gain wide acceptance for the very conclusions that mathematics helped them to reach. By applying numbers to the realm of man and medicine, Fliess had come up with concepts that were daring, original, and most important seemingly quite valid. Yet by burdening his published works with these encumbrances pages and pages of numerical tables, Charts, calculations, and proofs he frightened the medical profession as well as the public he sought to convince.

His critics said his presentation was too complex. His readers were either unable or unwilling to
wade through the multitude of statistics, and although no one could disprove his mathematical calculations, it might have appeared that they almost discouraged analysis.