18 ZOOLOGY. 



fatty adds.* The latter decomposes the sodium carbonate 

 and forms a soluble soap (i.e. a fatty salt, e.g. sodium 

 oleate). If, however, there is any calcium or magnesium 

 carbonate in the chyme, this will form an insoluble soap, 

 and so a certain proportion of the fatty acid will be wasted. 



13. Absorption in the Small Intestine. The pancreatic 

 juice is the last digestive juice of any importance that the 

 chyme meets with. By its action the remaining food- 

 materials have been changed into a soluble condition, and, 

 now absorption into the blood takes place] The absorption 

 of the various organic compounds takes place mainly in the 

 ilew&t whilejn the large intestine water^is absorbed and 

 the conteats~gradually become more and~mnrfl Tsnlid ; until 

 the characteristic appearance of faeces is produced. The 

 large " bubbles " of gas which are frequently seen distending 

 the rectum consist chiefly of hydrogen and methane (marsh- 

 gas) produced from the cellulose in the food by the action of 

 the abundant bacteria. 



The interior of the ileum has a shaggy or velvety appear- 

 ance, due to an abundance of small finger-like projections 

 of the wall, called villi. These villi, which project into the 

 liquid chyme, appear to be the active agents in absorption, 

 but the precise method of absorption is rather difficult to 

 understand. It will be sufficient for our purpose to say 

 that in each villus two kinds of vessels are found ordinary 

 blood-vessels (capillaries) and lacteals. The capillaries carry 

 off the sugar and proteids, while the lacteals take the 

 fat. It is a remarkable fact that, after all the trouble that 

 is taken to change proteids into peptones and fats into 

 glycerine and soap, the moment these have diffused into the 

 villi they seem to be re-converted into their original forms. 

 At all events, no peptones are found anywhere in the blood, 

 while the chyle, as the fluid in the lacteals is called, is (if 

 there was much fat in the food) quite milky from an 

 abundance of fat- droplets. What becomes of blood and 

 chyle we shall see in the next chapter. 



* Such as oleic acid. The adjective "fatty" means "chemically 

 related to fats," not " fat-like." All fats are compounds of glycerine 

 with some fatty acid. 



