_Second_ Economic Digestion-Ash (solid _excreta_), as a daily average for an adult of 140 lbs. (10 stone; 63.5 kilos), including moisture, when released, should not weigh more than two ounces (56.70 grams). An average of less than one half this amount of waste has been secured in test experiments. _Third_ The true test of healthy Z is absence of odour and completeness, ease and cleanliness of delivery. Frequency or otherwise, does not so much matter. Quantity too, is not so important; but with foul odour there is disturbance, strain and danger. The normal man is a cleanly being with all excreta inoffensive; and by these tokens he may be his own private judge. Why is it that barn-yards are tolerable to the human senses while open _dépôts_ of human excreta are fever-breeding nuisances and intolerable to beasts and humans alike? This curse of putrid excreta caused more deaths from enteric fever during the Boer War in South Africa than all other causes. It is equally a menace to health and even to life while being formed and carried in the body. _Fourth_ Offensive excreta are quite certain evidence of neglect of the self-controllable parts of our own nutrition. They are the tell-tale condemnation of ignorance or carelessness. Each person should learn to read the true bulletins of his health conditions in his waste-products of digestion. Z is the form the body _must_ assume to render emptying of the digestion-ash natural and easy. Man was built to squat on his heels in defecating, and sitting erect on a modern seat is like trying to force a semi-solid through a kinked hose. HEALTHY HUMAN EXCRETA ARE NO MORE OFFENSIVE THAN MOIST CLAY AND HAVE NO MORE ODOUR THAN A HOT BISCUIT. A. B.-Z. FIGURE TO ILLUSTRATE THE “DIVISION OF LABOUR” _First._ A Psychic Environment } This Mental State } involves: APPETITE (to select for) } ATTENTION (to prepare for) } DIGESTION APPRECIATION (to assist in) } (Absolutely necessary to secure secretion and flow of the digestive juices: Vide Pawlow and Cannon.) _Second._ B BUCCAL-DIGESTION } This MOUTH-TREATMENT } involves: MECHANICAL (teeth) } THOROUGHNESS CHEMICAL (salival) } (Absolutely necessary to secure complete digestion and avoid the putridity incident to bacterial decomposition: Vide Campbell and Van Someren.) INTERMEDIATE The twenty-three letters between “=B=” and “=Z=” represent but an inadequate proportion for the spelling of the enormous share Nature assumes in our welfare, marvellously performing her forty-seven forty-eighths share in the secret laboratory of the alimentary canal. _Third._ Z The true chemical end-point of digestion, by which each self-respecter may know how well he has respected his “A” and his “B,” and how faithfully he has performed his one forty-eighth share in the promotion of his own most fundamental interest. PREFACE TO 1906 EDITIONS