157 



mental activity contains no more phosphorus than that of other parts of 

 the body^not so much as the bones and teeth. Fish does not furnish 

 this element more abundantly than other animal foods. Good head 

 work like good hand work requires a good digestion, and as fish is easily 

 assimilated it may, for this very reason, be found of great value to 

 brain workers, especially if such do not take sufficient muscular exercise 

 to induce a vigorous digestion. 



Before bringing these lectures to a close I wish to gire you an 

 outline of the process of digestion, the changes that take place in 

 cooking food, and a few practical remarks drawn from a consideration 

 of the whole subject. 



Digestion. 

 Mastication or trituration of the food in the mouth serves by a 

 thorough division of the material to present a greater surface to the 

 solvent action of the digestive fluids. An increased digestion is the 

 result. Saliva, secreted by certain glands of the mouth, softens and 

 moistens the food and converts the insoluble starch into soluble 

 sugar. In this reaction the active principle is Ptyaline. 



The gastric juice, the secretion of the true peptic glands of the 

 stomach, has a physical and chemical action. It dissolves and disin- 

 tegrates the food, reducing it to a liquid condition, and converts tne 

 albuminoids into peptones, which are assimilated by the blood. Its 

 composition is : — 



Water ... 97.5 



Pepsin 1.5 



Hydrochlijric acid .5 



Salts 5 



100. o 

 It has an acid reaction. 



The intestinal digestion is promoted by the pancreatic juice, which 

 has an alkaline reaction. It has a fourfold function : — 

 (i) Converting starch into sugar. 



(2) Converting albuminoids into peptones. 



(3) The emulsification of fats. 



(4) Conversion of cane sugar into grape sugar. 



