INTESTINAL DIGESTION. 67 



CHAPTER IV. 



OF CALORIFACIENT OB INTESTINAL DIGESTION. 



Nature of Intestinal Digestion. Structure of the Intestine. Digestive Fluids of the Intestine. 

 The Pancreatic Juice. The Enteric Juice. Juice of Lieberkuhn. Secretion of Peyer's 

 Glands. Bik. Digestion of the Carbohydrates and Hydrocarbons. ^-Properties and Varie- 

 ties of Lactic Add. Doctrine of the Effects of Acidity and Alkalinity of the Digestive Juices. 

 Illustration of Intestinal Digestion from the making of Wine. MaJdng of Bread. Influence 

 of Heat over Ferments. Comparison of Gastric and Intestinal Digestion. Changes of the In- 

 testinal Contents. The Fozcal Residues. 

 



AFTER the chyme formed in the stomach has passed through the py- 

 loric valve into the small intestine, the influence of the gastric juice 

 continues for a certain time, even after the bile and pancreatic juices 

 have been reached. Since their action must be necessarily, in the first 

 instance, superficial, the interior of the mass is still undergoing stomach 

 digestion. 



But, setting aside this incidental result, which at the most can not be 

 of long duration, the digestive operation taking place in the ^ ature of in 

 part of the intestinal tract now under consideration is di- testinai diges- 

 rected to the heat-making food. 



The organ in which calorifacient digestion takes place may be de- 

 scribed as a tube bounded by two valves, the pyloric above structure of 

 and the ileo-coecal below. Its length may be estimated at the intestine, 

 about twenty feet. The digestive surface, making a due allowance for 

 its increase by reason of its valvular structure presently to be described, 

 can not be much under 3500 square inches. The dimensions of the ca- 

 lorifacient digesting surface are therefore far rreater than those of the 

 nutritive. 



The interior and acting portion of this tube presents two different 

 systems of apparatus, and is occupied in the discharge of two D 

 totally distinct functions, digestion and absorption. It is, ratus of intes- 

 perhaps, this double duty which demands so extensive a sur- tine ' 

 face, and not the necessities of heat-making digestion alone. 



Like the stomach, this tube consists of three coats a serous, a mus- 

 cular, and a mucous. The latter is gathered up in its inte- . 



. 11 c 11 i 11 , Action of the 



nor into numberless projecting folds the valvular conniven- vaivuise conni- 

 tes. These serve to increase the surface to which the food ventes - 

 is exposed, and perhaps afford a mechanical obstacle to its passing too 

 quickly forward. They tend also to break the continuous motion, and 

 bring the interior parts of the chyme to the surface. The onward move- 



