The science of life : fully illustrated in tone and line and including many diagrams

BOOK 1

lengthening, shortening, and swaying from side to side. It is through the villi that nutriment enters the blood. Each of these absorbent fingers is in contact outside with the digested food, while inside it passes a copious stream of blood. The cells of the villi are active, like the cells of the kidney or of the salivary glands. They lay hold of nutritive molecules in the gut and force them into the blood-stream. In this way proteins (broken down to amino-acids), carbohydrates (in the form of glucose or other equally simple sugar), and such substances as salt, which, being already simple enough, have undergone no digestion, are passed directly into the blood-stream. Thence they are carried to that very complicated organ, the liver.

Caecum

Fig. 31. The organs of Fig. 32 as they appear in the

rabbit.

The caecum is large in vegetable-feeding animals.

This dark-red large portentous organ plays a very central part in the internal activities of Mr. Everyman. We are all familiar with that hackneyed answer to the trite question: Is life worth living ?“That depends upon the liver.” And truly the working of this versatile but sensitive viscus is of primary importance to the chemistry of the body, and to the colour of the mood of which that body is either the medium or the material substance.

Let us rehearse the tale of the liver’s activities. We have already noted that it is a digestive gland, and described the digestive use of the bile in emulsifying fats and stimulating the pancreatic juice. The bile also contains excretory material due to the breaking up of old blood corpuscles, about

THE SCIENCE OF LIFE

CHAPTER 2

which we will not trouble ourselves here. Since the secretion of bile necessitates obvious anatomical structures—the presence of a bile-duct, tubules in the liver, and so forththis biliary secretion was the first of the liverfunctions to be recognized ; later, and only as a result of painstaking experimental research, was the chemical side of the liver’s activity brought to light. Now we realize that its chemical activity is even more important than its digestive. We have noted its action upon ammonia in our account of the kidneys. It can also deal with undesirable matters present in the blood from the gut—such as the substances produced by bacteria in the intestine during protein digestion. Its censorship is not exclusively chemical. If solid particles (such as bacteria themselves) make their way into the blood, certain of the liver-cells can actually lay hold of them and consume them. Next, the liver performs a great work of adJustment. If, for example, the sugar absorbed by the villi is in excess of that required by the body, it can store it in the form of glycogen, while if, as is often the case, there is insufficient fuel, but a surplus of protein, it can also break down the latter and convert the products into carbohydrate.

Because of its exposed positionexposed to anything that may get into the blood from the intestines, and also communicating with the intestine by means of an open ductthe liver is very liable to be deranged. That is a necessary consequence of its censoring duties. A number of parasitic organisms that cause various troubles, such as dysentery, in the bowels may penetrate to the liver, and produce abscesses. If Mr. Everyman is in the habit of overworking his censor—if, for example, he regularly consumes unnecessarily large amounts of alcohol—its sensitive specialized cells may be damaged and waste away, leaving too high a proportion of connective tissue, a condition known as cirrhosis. And the regular working of the liver may be upset in other ways. For example, inflammation of the bile-duct itself, or of the part of the intestine into which it opens, is very easily set up, a chill will do it. Then comes jaundice or a jaundiced condition. The bile cannot pass through the swollen, closed duct, so that the fats in the intestine are no longer dispersed, and therefore they are no longer digested. Moreover,