By far the best way of demonstrating the fallacy of the dictum that a prolonged fast only rids the body of superfluous excrementitious material, leaving the healthy tissues absolutely intact, is to take a comprehensive survey of the facts elicited by scientists in their careful study of the problem. For many years research on these lines was confined to German, French, and Italian investigators, but in more recent times the attention of British and American workers has been directed to the subject with valuable results. The main conclusions on the subject have been drawn from the accurate observations made upon professional starving men or "hungerkunstlers," chief among whom are Cetti, Breithaupt, and Succi.

At the very outset, however, it is necessary to define with some accuracy precisely what is meant by fasting. Briefly it may be considered as the deprivation of all or any of the elements essential to nutrition. It may therefore be (1) Complete, which means the absolute deprivation of food and water after a period of good nutrition, the only addition to the bodily resources being the 500 grams or thereby of oxygen inhaled in the daily respiration. In this form there is never a gain of weight. (2) Incomplete, which is usually held to cover a similar operation with the addition of a certain allowance of water. In this form there may or may not be a gain of weight, according to the amount of water consumed. For instance, in the case of Dr. Tanner, an American physician, who fasted for forty days, there was, after sixteen days of complete fasting and consistent loss of weight, a gain of 4 1/2 pounds brought about by drinking a considerable quantity of water.

The designation incomplete fasting may also be held to cover those cases where only one or two of the alimentary principles are withheld. These are, however, generally incapable of affording information of real value on fasting, although they may be of deep scientific interest otherwise; e.g., Straub fed a dog on dry meat powder mixed with fat, which necessitated a withdrawal of water from the tissues to dissolve the urea formed. The muscles lost 20 per cent. of their water and the protein metabolism was decidedly stimulated, but owing to the lack of fluid the digestive secretions decreased in amount, and all the food was vomited. In this way the experiment was reduced to one of complete fasting. Death from fasting occurs much more quickly where water is withheld, and in prolonged experiments it is usually administered in small quantities.

Von Noorden also classifies fasting experiments under two heads - (1) Acute Starvation, which includes both of the subdivisions already mentioned, and (2) Chronic Starvation, or malnutrition the result of weeks or months of insufficient nutrition. It is mostly in cases of this kind that the layman advises fasting as a therapeutic agency, and bases his deduction on facts drawn from their observation.