120 PHYSIOLOGY AT THE FARM. 



nerves, and covered with epithelium. These vary in size, 

 being either small and simple, or large and compound, or 

 even cleft into secondary papillae. Such papillse are de- 

 signed for various uses : some, as the papillae in the tongue, 

 have their office in the senses of taste and touch; some act 

 merely in a mechanical manner ; others have no other end 

 but to give an extension to the surface of the corium for the 

 development of a thick coating of epithelium. The villi be- 

 long in particular to the mucous coat of the small intestines. 

 They spring up so close to one another as to resemble the 

 pile or nap of cloth, whence the parts of the mucous membrane 

 on which they are developed obtain the name " villous," a 

 name, however, too often given to the mucous membrane of 

 the alimentary canal indiscriminately that is, without refer- 

 ence to the presence or absence thereon of such villi. The 

 villi in the mucous membrane of the small intestine are small 

 elevations or processes of the superficial part of the corium 

 or substance of the membrane invested with epithelium, and 

 enclosing blood-vessels and lacteals, which thus exist under 

 the most favourable circumstances for taking up nutrient fluids 

 from the bowel. 



These villi are well exhibited by the easy experiment of 

 immersing a piece of well-cleaned intestine in water, and 

 studying its surface with a simple lens. The most usual form 

 of the villi is a minute, flattened, triangular process : again, it 

 is conical or cylindrical, clubbed or filiform that is, at its 

 free extremity. At times, two or even three villi are united 

 together at their base. 



Their length (and here we draw on human anatomy) is from 

 l-4th to l-3d of a line, and the broad and flattened form 

 shows a breadth of l-6th or l-8th of a line, while they are 

 from l-24th to l-20th of a line thick. In the duodenum and 

 the jejunum they are most developed, both in number and 



