This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
Writing of a case that passed under his care, Dr. Jennings explains the rationale of fasting, thus: "The child has taken no nourishment for a number of days and may take none for many days to come; if it should live; yet there is nothing to be feared on this account. Take a healthy child from food while its vital machinery is in full operation, and it will use up its own building material and fall to ruin in two or three weeks; but in this case the system has been prepared for a long suspension of the nutritive function. There is now little action of the system generally, and consequently there is but little wear and tear of machinery; and like the dormouse, it might subsist for months on its own internal resources, if that were necessary, and everything else favored. The bowels too have been quiet for a number of days, and they might remain as they are for weeks and months to come without damage, if this were essential to the prolongation of life. The muscles of voluntary motion are at rest and cost nothing for their maintenance, save a slight expenditure of safe-keeping forces to hold them in readiness for action at any future time if their services be needed. So of all other parts and departments; the most perfect economy is everywhere exercised in the appropriation and use of the vital energies. It is an 'extreme case' and calls for extreme measures; but they are all conducted under a perfect law, which adapts with the most punctilious minuteness the means to the end."--Philosophy of Human Life, pp.159-160 (Italics mine, Author).