DIGESTION 357 



downward peristaltic movement. But even if this were not 

 the case, a few bacteria or their spores, passing through the 

 stomach with the food, would be enough to set up extensive 

 changes as soon as they reached a part of the alimentary 

 canal where the conditions were favourable to their develop- 

 ment. Indeed, from the time when the first micro-organism 

 enters the digestive tube soon after birth, it is never free 

 from bacteria; and their multiplication in one part of it 

 rather than another depends not so much on the number 

 originally present to start the process, as on the conditions 

 which encourage or restrain their increase. 



The fats are broken up into their fatty acids and glycerine 

 by the fat-splitting ferment of the pancreatic juice. The 

 acids will form soaps with alkalies wherever they meet them 

 in the intestinal contents, or even in the mucous membrane. 

 A portion of those soluble soaps may be immediately ab- 

 sorbed ; the rest may aid in the emulsification of the fats not 

 yet chemically decomposed, and thus greatly hasten the fat- 

 splitting action of the pancreatic juice. The starch and 

 dextrine which have escaped the action of the saliva are 

 changed into maltose by the amylopsin. A little dextrine 

 may be absorbed as such (Bleile). 



The succus entericus, as an alkaline liquid, aids in lessen- 

 ing the acidity of the chyme and establishing the reaction 

 favourable to intestinal digestion. It will invert any cane- 

 sugar which may reach the intestine ; but it cannot be 

 doubted that cane-sugar may be absorbed by the stomach, 

 being inverted by the hydrochloric acid of the gastric juice 

 or by inverting ferments taken in with the food, or on its 

 way through the gastric walls. 



Upon the whole no great amount of water is absorbed in 

 the small intestine, or at least the loss is balanced by the 

 gain, for the intestinal contents are as concentrated in the 

 duodenum as in the ileum. But as soon as they pass beyond 

 the ileo-caecal valve, water is rapidly absorbed, and the 

 contents thicken into normal faeces, to which the chief con- 

 tribution of the large intestine is mucin, secreted by the vast 

 number of goblet-cells in its Lieberkuhn's crypts. 



Bacterial Digestion. So far we have paid no special attention 



