392 



STRUCTURE OF THE LARGE INTESTINE. 



Nerves Of the Intestine. Thoughout the whole intestinal tract, there exists 

 the plexus myentericus of Auerbach (Fig. 154), lying between the longitudinal 

 and circular muscular coats. This plexus consists of non-medullated nerves with 



groups of ganglionic cells at the nodes. Fibres 

 are given off by it to the muscular coats. 



Connected by branches with the foregoing and 

 lying in the sub-mucosa, is the plexus ofMeissner, 

 which is much finer, the meshes being wider, the 

 nodes smaller, but also provided with ganglionic 

 cells. It supplies the muscular fibres and arteries 

 of the mucosa, including those of the villi. It 

 also supplies branches to Lieberkuhn's glands 

 (Drasch). Compare Figs. 131 and 132. 



[Structure of the Large Intestine. It has 



four coats like those of the small intestine. The 

 serous coat has the same structure as that of 

 the small intestine. The muscular coat has 

 external longitudinal fibres occurring all round the 

 gut, but they form three flat ribband-like longi- 

 tudinal bands in the caecum and colon. Inside 

 this coat are the circular fibres. The sub- 

 mucosa is practically the same as that of the 

 small intestine. The mUCOSa is characterised 

 by negative characters. It has no villi and 

 no Peyer's patches, but otherwise it resembles 

 structurally the small intestine, consisting of a 

 basis of adenoid with the simple tubular glands 

 of Lieberkuhn (Fig. 155). These glands are very 

 numerous and somewhat longer than those of the 

 small intestine, and they always contain far 

 more goblet-cells. The cells lining them are 

 devoid of a clear disc. Solitary glands occur 

 throughout the entire length of the large intes- 

 tine. At the bases of Lieberkuhn's glands is 

 the muscularis mucosce. The blood-vessels and 

 nerves have a similar arrangement to those 

 the stomach.] 



Fig. 155. 



Lieberkuhn's gland from 

 large intestine (dog). 



the 



in 



191. Absorption of the Digested Food. 



The physical forces concerned are endosmosis, diffusion, and filtration. 



All the constituents of the food, with the exception of the fats, which in part 

 are changed into a fine emulsion, are brought into a state of solution by the digestive 

 processes. These substances pass through the walls of the intestinal tract, either 

 into the blood-vessels of the mucous membrane or into the beginning of the 

 lymphatics. In this passage of the fluids two physical processes come into play 

 endosmosis and diffusion as well as filtration. 



I. Endosmosis and diffusion occur between two fluids which are capable of 

 forming an intimate mixture with each other, e.g., hydrochloric acid and water, 

 but never between two fluids which do not form a perfect mixture, such as oil and 

 water. If two fluids Capable of mixing with each other, but of different com- 

 positions, be separated from each other by means of a septum with physical pores, 

 (which occur even in a homogeneous membrane), an exchange of the constituents in 



