12 TEXT-BOOK OF PHYSIOLOGY 



Palmitic acid occurs in the form of white, glistening scales or needles, 

 melting at 62C. 



Oleic acid is a clear, colorless liquid, tasteless and odorless when pure. 

 It crystallizes in white needles at oC. 



If this saponification takes place in the presence of an alkali e.g., 

 potassium hydroxid or sodium hydroxid the acid produced combines 

 at once with the alkali to form a salt known as a soap, while the glycerin 

 remainsjn solution. The reaction is as follows: 



3 KHO + 3 C 18 H 34 2 - 3 KC 18 H 33 2 + 3 H 2 O 

 Potassium Hydroxid. Oleic Acid. Potassium Oleate. Water. 



All soaps are, therefore, salts formed by the union of alkalies and fat 

 acids. The sodium soaps are generally hard, while the potassium soaps 

 are soft. Those made with stearin and palmitin are harder than those 

 made with olein. If the soap is composed of lead, zinc, copper, etc., it is 

 insoluble in water. 



Emulsification. When a neutral oil is vigorously shaken with water 

 or other fluid, it is broken up into minute globules that are more or less 

 permanently suspended; the permanency depending on the nature of the 

 liquid. The most permanent emulsions are those made with soap solutions. 

 The process of emulsification and the part played by soap can be readily 

 observed by placing on a few cubic centimeters of a solution of sodium 

 carbonate (0.25 per cent.) a small quantity of a perfectly neutral oil to which 

 has been added 2 or 3 per cent, of a fat acid. The combination of the acid 

 and the alkali at once forms a soap. The energy set free by this combination 

 rapidly divides the oil into extremely minute globules. A spontaneous 

 emulsion is thus formed. 



Lipoids. This term has been applied to a group of substances of 

 diverse chemical composition, which are soluble in ether and alcohol and 

 in this respect resemble the fats for which reason they were termed lipoids. 

 Lipoids are found in the protoplasm of the cells of many tissues and 

 especially nerve tissues. In many cells they constitute a part of the envel- 

 oping membrane or surface. According to their chemical composition 

 they maybe divided into several groups, viz.: i. Those consisting of 

 carbon, hydrogen and oxygen, e.g., cholesterol, the molecular composition 

 of which is C27H45OH. 2. Those containing in addition nitrogen, the 

 galactosides, so called because they yield on decomposition a reducing 

 sugar termed galactose. 3. Those containing carbon, hydrogen, oxygen, 

 nitrogen, and phosphorus, the so called phosphatids, e.g., lecithin, kepha- 

 lin, and sphingomyelin. The phosphatids differ among themselves in the 

 relative amounts of nitrogen and phosphorus they contain. 



THE PROTEINS 



The proteins constitute a group of organic bodies which are found in both 

 vegetable and animal tissues. Though present in all animal tissues, they 

 are especially abundant in muscles and bones, where they constitute 20 

 per cent, and 30 per cent, respectively. Though genetically related, and 

 possessing many features in common, the different members of the protein 

 group are distinguished by characteristic physical and chemic properties 

 which serve not only for their identification, but for their classification into 

 more or less well-defined groups. 



