484 



MANUAL OF HISTOLOGY. 



ance, which undigested albumen does not possess. In contradistinction 

 to the latter, then, these peptones might be designated as albuminates 

 capable of being absorbed. Owing, however, to the extreme difficulty of 

 the subject, there still exists up to this very hour a great difference of 

 opinion among physiologists as to the nature of peptone, in spite of the 

 exertions of very excellent observers (Brucke, Meissner). 



254. 



The small intestine, with its serosa and well-known double layer of 

 muscle fibres, presents, as regards its mucous membrane, a far more 



Fig. 470. From the small intestine of the vab- Fig. 471. Vertical section of the mucous mem- 

 bit, a, tissue of the mucous membrane; 6, brane of the small intestine of a cat. a, the 

 lymphatic canal; c, an empty transverse sec- glands of Lieberkuhn; b. villi. 

 tion of a gland of Lieberkuhn; d, another of 

 the same occupied by cells. 



complicated structure than that of the stomach. This membrane, in the 

 first place, is thrown out into a multitude of crescentic duplicatures, 

 known as valvulce conniventes Kerkringii, and is covered in the next by 

 innumerable small conical processes, the villi intestinales. By this 

 arrangement of valves and tufts, an enormous increase of surface is 

 obtained. We find, further, in the tissue of the mucosa, two forms of 

 glands, namely, the racemose mucous glands of Brunner, and the tubular 

 of Lieberkuhn, to which may be added the lymphoid follicles, either 

 single or in groups, known as the solitary and agminated glands of 

 Peyer. 



But the tissue of the mucous membrane itself (fig. 470), is also different 

 in texture from that of the stomach. Thinner, and supplied with the 

 muscularis mucosce, it no longer presents the character of ordinary fibrous 

 tissue, as does that of the stomach as a rule. It consists rather of 

 reticular connective-tissue, containing, entangled in its interstices and 

 meshes, an abundance of lymphoid cells, and only assuming a more or 

 less homogeneous membranous structure towards the gland cavities and 

 towards its free surface, whilst at other points, as, for instance, near the 

 surface of large vessels, it appears to be made up of longitudinal fibres. 

 This tissue of the mucous membrane varies also to a certain extent, 

 according to the different species of animals. 



The villi commence on the intestinal aspect of the pylorus, flat and 

 low at first, and increasing gradually in height until they assume a 

 conical or pyramidal form, which merges step by step, as we progress 

 downwards, into a slender tongue-like figure. They stand tightly packed 



