98 STUDIES IN PHYSIOLOGY 



in the following experiments : Put into a test tube a small 

 amount of olive oil or melted butter, add water and shake. 

 The oil is broken up into small spheres and mingled with 

 the water during the process of shaking. When the test 

 tube is set aside, however, the oil rises to the surface, show- 

 ing that the two liquids will not remain combined. 



If, now, a solution of caustic, soda or other alkali be 

 shaken up with the oil and water, the mixture assumes a 

 milky appearance, and the oil does not then rise to the top 

 in a clear layer as it did after being shaken with the water. 

 Fat, when thus mixed with an alkali, forms an emulsion. 

 If a drop of this mixture is examined with a compound 

 microscope, tiny spheres of fat are seen floating about in a 

 colorless liquid. Each little sphere is inclosed by a thin 

 covering of the alkali, and thus the fat droplets are kept 

 separate from each other. Water will not form this thin 

 covering, nor will an acid. For this reason, fats are not 

 emulsified in the stomach. They are acted upon only by 

 the strongly alkaline juices of the intestine. A still better 

 emulsion can be formed by shaking the oil with raw white 

 of egg. In this case the fat globules are surrounded by a 

 thin layer of albumin. Milk is an emulsion consisting 

 of fat (cream) and of liquid proteids. 



When the emulsion, made by mixing the oil and the alkali, 

 is heated, a chemical change takes place and some of the 

 fat is converted into soap and glycerin. Both of the latter 

 are readily soluble in water, and so can be easily taken up 

 by the blood. The pancreatic juice acts upon fats in both 

 the ways we have been describing. Since it is alkaline, it 

 forms an emulsion. It can likewise change fats into soap 

 and glycerin. When these compounds get into the blood, 

 however, they are changed again into fats. 



11. THE LIVER 



Position, Form, Size The human liver is the largest gland 



of the body, weighing three to four pounds. It lies toward 



