VI FAT EMULSIFIED 265 



solved, and made diffusible and so prepared for their 

 passage into the vessels. 



As the food is thrust along the small intestines by the 

 grasping action of the peristaltic contractions, the digested 

 matter which it contains is absorbed, that is, passes away 

 from the interior of the intestine into the blood-vessels 

 and lacteals lying in the intestinal walls. 



All the way down the small intestines, the proteins, 

 carbohydrates, and fats of a meal are being dissolved 

 or otherwise changed, and passing away into the lacte-xls 

 or blood-vessels. So that, by the time the contents of 

 the intestine have reached the ileo-csecal valve, a great 

 deal of the nutritious matter has been removed. Still, 

 even in the large intestine, some nutritious matter has 

 still to be acted upon ; and we find that in the caecum 

 and commencement of the large intestine, changes are 

 taking place, apparently somewhat of the nature of 

 fermentation, whereby the contents become acid. But 

 these changes do not appear to be brought about by any 

 soluble ferments secreted by tlie walls of this intestine ; 

 on the contrary they are largely the result of the activity 

 of certain minute organisms or organised ferments 

 (bacteria, &c.). 



In herbivora a considerable quantity of the cellulose 

 they eat does not reappear in the fseces and a small 

 amount may be digested in man. The digestion of 

 cellulose probably takes place in the large intestine and 

 is brought about by the action of micro-organisms. 



One marked feature of the changes undergone in the 

 large intestine is the rapid absorption of water. Whereas 

 in the small intestine, the amount of fluid secreted into 

 the canal about equals that which is removed by absorp- 

 tion, so that the contents at the ileo-csecal valve are 

 about as fluid as they are in the duodenum ; in the large 

 intestine on the contrary, especially in its later portions, 

 the contents become less and less fluid. At the same 

 time a characteristic odour and colour are developed, and 



