NUTRITION , .-.,,,, ,, , JQI 



Under ordinary circumstances, water forms about half the 

 total weight of the body. The dry matter consists almost 

 entirely of fat and protein. The percentage of mineral matter 

 is relatively small. 



Functions of the Organs. The heart and lungs are 

 respectively the active organs of circulation and respiration. 

 The abdominal viscera are mainly concerned with the digestion 

 and absorption of the food. The material absorbed is dis- 

 tributed to all parts of the body by the blood. Excess of 

 water, certain products of katabolism, soluble salts, etc., are 

 eliminated from the blood by the kidneys and discharged as 

 urine. The chief functions of the nerves are sense (perception) 

 and control. 



The process of digestion begins in the mouth. By masti- 

 cation the food materials are mechanically disintegrated and 

 mixed with saliva. This fluid has a faintly alkaline reaction 

 and contains a ferment called ptyalin an amylase which 

 acts upon starchy materials and converts them into sugars 

 (p. 87). 



In the stomach, the food is acted on by the gastric juice 

 which has an acid reaction. It contains a small amount (from 

 0-2 to 0-5 per cent.) of hydrochloric acid and several enzymes. 

 Pepsin, the most important of these, is a proteolytic ferment. 

 It acts upon proteins and converts them into the soluble, 

 diffusible proteoses and peptones (p. 71). 



From the stomach, the partially digested food passes 

 through the duodenum, where it is mixed with the secretions 

 of the liver and the pancreas, and so into the intestines. 



The secretion from the liver is called bile. Like the 

 saliva, it is faintly alkaline, and it contains ferments of the 

 lipase type which act upon fats, and saponify them (p. 40). 

 Apparently the fats are first emulsified, i.e. broken up into 

 extremely minute particles which remain diffused through the 

 aqueous fluid, but they are probably all saponified before 

 absorption. 



The pancreatic juice is also alkaline, and contains several 

 ferments which enable it to perform, to some extent, the 

 functions of all the digestive juices previously mentioned. It 



