atic secretion jilso acts in the same way as does the bile of the liver 

 upon the fat, bringing it into a very finely divided condition. 



The action of the intestinal secretion is not fully understood. It 

 contains however a small amount of ptyalin which changes starchy 

 matters into sugar. 



In addition to the several secretions mentioned, various bacteria play 

 a considerable part in the process of digestion in the small intestine. 

 They decompose or break down more or less protein, convert starch 

 into sugar, and decompose the cellulose which hitherto has not been 

 acted upon, into a variety of simpler substances. 



To recapitulate briefly : The food acted upon by the various 

 secretions of the stomach and intestines as well as by bacteria is 

 converted into soluble substances. This rather thick liquid has a 

 milky ap|)earauce and is termed chyle. The food in this soluble 

 condition is takon up by a multitude of so called epithelial cells or villi, 

 with which the intestines are lined, and carried with more or less 

 change into the blood, there to serve as a source of nourishment. 

 That portion of the feed which has not been made soluble, passes on 

 into the large intestine, and is finally excreted as faeces*. 



WAYS IN WHICH THE DIFFERENT GROUPS OF DIGESTED FEED 

 CONSTITUENTS ARE USED. 



After the protein, carbohydrates, and fat, have been made soluble 

 and takon into the blood, they are transported to the multitude of 

 cells composing the body. The vital force of the cell — the cell juice 

 or protoplasm — shatters or breaks the larger part of them into 

 simpler substances thus liberating heat and vital energy. This 

 process is completed by the oxygen of the blood still further decom- 

 posing them into carbonic acid and water, which are transported to 

 the lungs and exhaled. All three groups then, serve as sources of 

 heat and energy. 



Special uses and characteristics of the protein : Protein is perhaps 

 a source of fat, and is the only source of Jiesh. It is also — in the 

 form of casein or curd — a very prominent constituent of milk. 

 Before it becomes flesh or casein it is more or less reconstructed by 

 the cells. When protein is broken up and transformed into heat and 

 energy, a considerable portion of its carbon and hydrogen is 



*The faeces or solid excrement, is nothing more than the uncHgested part of the 

 feed. It contains one-half of the nitrogen, and three-fourths of the phosphoric 

 acid excreted by tlie animal daily. 



