26 



APPLIED PHYSIOLOGY 



28. Saponification of fats. When fat is boiled with soda or 

 potash it is broken up into a small amount of glycerine and a large 

 amount of a substance called a fatty acid. The fatty acid unites with 

 the soda or potash to form soap. When by any means fat is broken 

 up with soda or potash, forming soap, the process is called saponifica- 

 tion. Both soaps and emulsions are continually being formed during 

 the digestion of fat. 



29. Use of fat. The, fat of the body is a living garment, 

 retaining heat and protecting the body from the cold, and 

 rounding out the rugged outlines of the bones and muscles. 

 It is a cushion, protecting the internal organs from injury. 

 It is also a store of food to be used in sickness when food 

 cannot be eaten. The fat which is eaten is used up in 

 warming the body. Thus fat acts as a food, as armor for 

 the body, and as useful and ornamental clothing. About 

 three ounces of fat must be eaten each day. 



30. Starch and sugar. Starch is produced almost en- 

 tirely by plants and is stored in the form of little grains 



which will not dis- 

 solve in cold water. 

 Grains of potato starch 

 appear like oyster 

 shells and show dis- 

 tinct markings as 

 though they were built 

 up in layers. It is 

 supposed that starch 

 grains grow by deposits 

 of successive layers of starch between which are layers of 

 a waterproof substance called cellulose or plant connective 

 tissue. When the grains are boiled, they swell and burst 

 and then dissolve, forming a paste. As a plant grows, it 

 uses the starch in building up sugar, wood, cotton, cellu- 

 lose, and other plant substances. Starch, sugar, wood, cot- 



starch Grains (X40o). 

 a, of potato. b, of corn. 



