[5] For a knowledge of the structure and function of the mucous lining of the stomach and intestines, and of the tributary glands, such as the liver and pancreas, which is important to a thorough understanding of digestion, the reader is referred to _Let’s Be Healthy_, of this series. In this will be found a study of the secretion of digestive juices, the conditions favoring normal secretions, etc. [6] Hereafter, in speaking of sugar, after it has been absorbed into the blood, the reader will bear in mind that the term refers not only to digested sugar, consumed as such, but also to digested starches (maltose). [7] See _Let’s Be Healthy_, by Susanna Cocroft. CHAPTER VI ORGANS AND CONDITIONS AFFECTING DIGESTION The purpose of this chapter is to show the work of other than the digestive organs in assimilation, construction, and elimination. The _liver_ is commonly called the chemical workshop of the body. The digested food is carried by the blood (portal veins) to the liver as soon as it is absorbed from the alimentary canal. As the food materials filter through the blood capillaries, between the liver cells, several substances are absorbed, particularly sugar, which is changed into the animal starch called _glycogen_. It is held in the liver for a few hours in this form and is then redigested and gradually given to the blood in the form of sugar. While the conversion of the sugar is one prominent function of the liver, it also acts on the proteins—not as they are first passed through the liver in the blood, but as they are returned to the liver from the muscle tissue, partly oxidized and broken up into simpler products. The liver cells absorb and further oxidize and combine them into nitrogenous waste, which the kidneys throw off in urea. The liver and the spleen also dissolve the pigment or coloring matter out of the red blood corpuscles. As these become useless, they are broken up in the liver and the spleen. The iron is retained by the liver cells and the remainder is thrown off in the bile. The liver is on guard for all poisons which pass through it in the blood. The large part of these toxic substances are absorbed through the alimentary canal with the foodstuffs. Many of them are the result of the fermentation of foods which are not digested so promptly or so thoroughly as they should be, on account of an insufficient secretion of digestive juices, or on account of a failure to secrete them in normal proportions, due to inactivity of the stomach and intestines. Nature thus supplies a guard to oxidize, or break down these poisons and make them harmless, so that normally they do not affect the nerves and the blood stream, and, through these, the entire system. The necessity of correct habits of deep breathing will be readily seen here, because oxygen is required to break down the poisons as well as to oxidize the worn-out tissues.