FUNCTIONS OF THE LARGE INTESTINE 723 



whereas in the caecum the acids are neutralised by the secretion of alkalies 

 and the reaction remains practically, neutral. The products of digestion 

 of cellulose, as well as the contents of the vegetable cells set free by the 

 solution of the cell walls, are gradually absorbed by the walls of the large gut. 

 In carnivora the large intestine has very unimportant functions to discharge 

 in digestion and absorption. The proteins of meat are practically entirely 

 absorbed by the time that the food has arrived at the ileocolic valve, and the 

 same applies to fat. In man the importance of the large intestine will vary 

 with the nature of his food. Under the conditions of civilised life the food 

 material is almost entirely absorbed by the time that it reaches the lower end 

 of the ileum. If, however, a large quantity of vegetable food be taken, such 

 as fruit or green vegetables, or cereals roughly prepared and coarsely ground, 

 a considerable amount of material may reach the large intestine unabsorbed. 

 A certain proportion of this may undergo absorption in the large intestine, 

 while the rest will pass out with the faeces, increasing their bulk. 



It is hardly possible to speak of a secretion by the mucous membrane 

 of the large intestine. In herbivora alkaline carbonates are secreted to 

 neutralise the acids produced in the bacterial fermentation of the food, but 

 the processes of absorption and secretion keeping pace, there is no accumu- 

 lation of the products of secretion in the intestine. A section of the mucous 

 membrane shows a number of simple tubular glands. The greater number of 

 the cells lining these glands are typical ' goblet ' cells and contain plugs of 

 mucin. The secretion of mucus not only aids the passage of the faeces 

 along the gut, but probably impedes the propagation of the bacteria which 

 are present in countless numbers in the faeces. This may account for the 

 fact that although bacteria are so numerous in the faeces, it is difficult to 

 cultivate any large numbers most of them being dead. 



As an absorbing organ the large intestine of man is of little importance. 

 From observations on fistulae in man it has been calculated that about 500 

 c.c. of water pass the ileocolic valve in the twenty- four hours. Of these about 

 400 c.c. undergo absorption in the large intestine. The absorption of any 

 of the food substances by this part of the gut is much slower than that which 

 takes place on introduction by the mouth. Feeding by nutrient enemata 

 is thus always very inadequate. In some cases after the introduction of 

 large enemata into the large intestine a certain amount may escape back- 

 wards into the ileum and may there undergo absorption. The isolated large 

 intestine of man is able to absorb only about six grammes of dextrose per 

 hour and about 80 c.c. of water. If egg albumin or caseinogen solutions 

 be introduced by the rectum no absorption can be detected after several 

 hours. In observations extending over a considerable time some disappear- 

 ance has been observed of proteins and emulsified fats, as well as of boiled 

 starch. This was due, however, to the action of bacteria on these substances, 

 and was probably of very little value for the nourishment of the individual. 

 Feeding by nutrient enemata is thus merely a method of slow starvation. 

 If it is employed it should be limited to administration of water, salines, 

 or solutions of glucose. 



