A THREATENED FACTORY 213 



bowel still remains a mystery — the part which is most 

 liable to become the seat of an acute disorder. This is 

 the appendix. It is shaped like a narrow test-tube and is 

 usually about four inches in length, and about a quarter 

 of an inch in diameter. Its blind end is free pointing 

 towards the pelvis ; its mouth opens on the interior of 

 the caecum (fig. 44B). Its muscular coats are strong and 

 contraction waves sweep slowly along them. It beats with 

 a slow rhythm. It receives material from the caecum which 

 it works upon, but what digestive changes it effects or 

 what role it plays is not known. It is a highly specialised 

 part, it has often to be removed by the surgeon on account 

 of disease and the human machine appears to manage 

 perfectly well without it. That does not mean that it is 

 a useless or vestigial structure. We may lose an eye ; 

 to our friends we seem to get along just as well as before. 

 The sufferer, however, knows that such is not really the 

 case ; careful observation shows him that there are many 

 things he cannot make out so well as when he had both 

 his eyes. All that we can safely say about the appendix is 

 that it is better to be without one than to possess one which 

 is diseased and therefore liable to cause death. But that 

 it should be so frequently invaded by disease-producing 

 germs will be understood when we look more closely at 

 the nature of the digestive processes carried out in the 

 caecum. 



The reader must not think that the part of the human 

 machine we are now dealing with is one of minor im- 

 portance — a mere economical contrivance which Nature 

 has fitted to the human machine in order that the pro- 

 ducts which escape from the small bowel may be saved. 

 The great bowel is one of the largest laboratories in the 

 human body. When laid open and spread out it forms 

 a long narrow sheet, the width diminishing as it passes 

 from the caecal to the anal extremity. In an adult man 

 the average width of the sheet is about 6 inches, its 

 average length about 70 inches. Its lining membrane 

 therefore exposes a surface for the absorption of food 

 products of about 420 square inches. This, although 



