In order that we may understand much that takes place within the fasting organism, it is necessary that we have an understanding of the process of autolysis, which, although very common in nature, has been all but overlooked by physiologists generally. We have previously mentioned the fact that the vital or functioning tissues of the fasting organism are nourished off the food reserves stored in the body. These reserves are stored as rather complex substances, such as sugar (glycogen), fat, protein, etc., and are no more fitted for entrance into the bloodstream and use by the cells than are the fats, proteins and carbohydrates of another animal, or another food. Before they can be taken up by the circulation and assimilated by the cells, they must first be digested.

Let us begin with a familiar example of the digestion and absorption of a part of a living organism by the organism itself. In the process of becoming a frog the tadpole grows four legs. After these are fully formed, he no longer has use for the tail that served so well in the tadpole stage, so he proceeds to get rid of it, not by shedding it as is popularly supposed, but by absorbing it. The tail is made up of muscle, fat, nerves, skin, etc. To absorb these structures, they are digested in the same way that fat and muscle are digested in the digestive tract. By the action of the appropriate enzymes the proteins and fats are broken down into their constituent amino and fatty acids. Only thus are they fit to re-enter the circulation. Only as fatty acids and amino acids can they be re-used with which to nourish other structures of the body of the frog.

During the period when the tail of the ex-tadpole is being absorbed, the young frog does not eat. Indeed, it ceases to eat when the forelegs come into view. Fasting may be essential to the absorption of the tail, at least it hastens the process, for it compels the utilization of the tail as food with which to nourish the vital tissues of the fasting frog.

We may liken this process to that of the eating of its skin by the toad. Toads molt several times yearly. They swallow their molted skin after they emerge from it. To make use of the molted skin, the toad must first digest it. Its proteins and fats must be reduced to simple acceptable compounds, such as amino acids and fatty acids. This is done in this instance in the stomach and intestine of the toad. But in the case of the fasting frog digesting its tail, the work is done within the tail itself.

The word autolysis (a-tol-i-sis) is derived from the Greek and means, literally, self-loosing. It is used in physiology to designate the process of digestion or disintegration of tissue by ferments (enzymes) generated in the cells themselves. It is a process of self-digestion--intra-cellular digestion.

A number of autolytic (a-to-lit-ik) enzymes are known and are included under the general terms, oxidases and peroxidases. Physiologists know that proteolytic (protein digesting) enzymes are formed within many, if not in all living tissues. Apparently every tissue turns out its own enzyme, which, probably, under all ordinary circumstances of life, is employed in the regular processes of metabolism. Under other conditions the enzymes may be employed to digest the substances of the cells themselves. In their Textbook of Physiology (1946 edition) Zoethout and Tuttle mention that under certain experimental conditions the unrestrained activities of the enzymes normally present in the liver (proteases, lipases, carbohydrases) digest the proteins, carbohydrates, and fats of the liver. In normal life this digestion of the liver does not occur. These various intra-cellular enzymes play a conspicuous part in the metabolism of food substances; that is, in the normal or regular function of nutrition or metabolism.

A few familiar examples of autolysis will prepare the reader to understand its use in "disease." The phenomena of fasting supply many examples of the control the body exercises over its autolytic processes. For example, tissues are lost in the inverse order of their usefulness--fat and morbid growths first, and then the other tissues. These tissues (fatty tissue, bone marrow, etc.) and food substances (glycogen) are not fit to enter the blood stream before they are acted upon by enzymes. Indeed, human fat, or human muscle, is no more fitted to enter the circulation without first being digested, than is fat or muscle from the cow or sheep. Glycogen (animal starch), stored in the liver, must be converted into a simple sugar before it can be released into the blood stream. This conversion is accomplished by enzymic action.

The manner in which an abscess "points" on the surface of the body and drains its septic contents on the outside is well known to every one of my readers. What is not generally known, is that this "pointing" on the surface is possible only because the flesh between the abscess and the surface is digested by enzymes; that is, it is auto-lyzed and removed.

The absorption of the bone-ring support established about the ends of a fracture is made possible by the autolytic disintegration of the bone-ring. The re-arrangement of materials in pieces of planaria and the dissolution of the pharynx in the piece containing this, to form a new one to fit the new size, as described elsewhere, is made possible by autolysis.