DIGESTION 103 



" crypts of Lieberkiihn." Their relation to the wall might be 

 exemplified by taking a block of dough about 6 inches thick 

 and pushing a pencil vertically into it almost down to the table 

 on which it rests. The holes should be made as close together 

 as possible, since, especially in the stomach, extremely little 

 tissue intervenes between the tubes of gland-cells. If the 

 piece of dough were placed upon a folded cloth, the cloth 

 would represent the muscularis mucosae, a layer properly 

 regarded as a constituent of the mucous membrane. The 

 fibres of this coat are disposed in two or three sheets, the 

 fibres of one sheet crossing those of the next. By their con- 

 tractions they squeeze the ends of the crypts, and probably 

 wobble them about, expelling their secretion. Beneath the 

 muscularis mucosse is a layer of connective tissue, the rub- 

 mucosa, which contains abundant lymphatic channels, blood- 

 vessels, and nerves. At the pyloric end of the stomach, the 

 tubes of gland-cells tend to pierce the muscularis mucosse. In 

 the first part of the duodenum, certain tubes, having pierced this 

 layer, branch in the submucosa. A layer of racemose glands 

 is thus formed the glands of Brunner. Outside the sub- 

 mucosa is the muscular coat proper, composed of plain muscle- 

 fibres, except in the upper part of the oesophagus, where the 

 fibres are striated. It consists of an inner and an outer sheet, 

 the fibres being disposed circularly in the inner, longitudinally 

 in the outer sheet, with a slight departure from this regular 

 arrangement in the wall of the stomach. On its outside the 

 canal is invested by peritoneum, a layer of flattened epithelial 

 cells supported by connective tissue. The abdominal wall also 

 is lined with peritoneum. The smooth moist surface of the 

 peritoneum covering the intestines glides on the peritoneum 

 lining the abdominal wall. Between the two is a " potential " 

 space. In dropsy, fluid accumulates within this space. In a 

 healthy condition the apposed surfaces are merely moist. 



The movements of the intestines are of two kinds. At all 

 times they exhibit swaying movements, in the production of 

 which the longitudinal fibres play the chief part, although the 

 circular fibres also contract. The object of this undulation is 

 to thoroughly mix the contents of the gut with its secretions. 

 If pills of subnitrate of bismuth are administered, and their 

 progress observed by the aid of Rontgen rays, they are seen to 



