94 FATS AND ALLIED SUBSTANCES [ch. 



Expt. 93. ReactioTis of soaps, (a) Take some of the soap which has been filtered 

 off and shake up with water in a test-tube. A lather should be formed. (6) Make 

 a solution of a little of the soap in a test-tube and divide it into three parts. To each 

 add respectively a little barium chloride, calcium chloride and lead acetate solutions. 

 The insoluble barium, calcium and lead salts will be precipitated. (The curd which 

 is formed in the case of soap and hard water is the insoluble calcium salt.) Thirdly, 

 take the remainder of the soap and acidify it with dilute acid in an evaporating dish, 

 and warm a little on a water-bath. The soap is decomposed and the fatty acids are 

 set free and rise to the surface. 



JExpt. 94. Reactions of fatty acids, (a) Try the solubilities in ether and alcohol 

 of the acids from the previous experiment. They are soluble, (b) Shake an alcoholic 

 solution of the fatty acids with dilute bromine water. The colour of the bromine is 

 discharged owing to the bromine forming additive compounds with the unsaturated 

 acids. 



The question of the metabolism of fats in the plant is a very com- 

 plicated one and has not yet been satisfactorily investigated. All plants 

 may have the power of synthesizing fats, and a great number, as we 

 have seen, contain large stores of these compounds in the tissues of the 

 embryo, or endosperm, or both. The point of interest is that of tracing 

 the processes by which these fats are synthesized, and are again hydro- 

 lyzed and decomposed. The products of decomposition may serve for the 

 synthesis of other more vital compounds as the embryo develops, and 

 before it is able to synthesize the initial carbohydrates, and to absorb 

 the salts requisite for general plant metabolism. 



One fact seems fairly clear, namely that when fat-containing seeds 

 germinate, an enzyme is present in the tissues which has the power of 

 hydrolyzing fats with the formation of fatty acids and glycerol. Such 

 enzymes are termed lipases. 



The lipase which has been most investigated is that which occurs 

 in the seeds of the Castor-oil plant (Ricinus communis). It has been 

 shown that if the germinating seeds are crushed and allowed to auto- 

 lyze (p. 20) in the presence of an antiseptic, the amount of fatty acid 

 increases, whereas in a control experiment in which the enzyme has 

 been destroyed by heat, no such increase takes place (Reynolds Green, 

 13, 14). 



Investigation has shown the enzyme to be present also in the resting 

 seed, but in an inactive condition as a so-called zymogen (Armstrong, 

 4, 5, 6, 7). The zymogen is considered to be a salt and, after acidifica- 

 tion with weak acid, the salt is decomposed, and the enzyme becomes 

 active. After the preliminary treatment with acid, however, the enzyme 

 is most active in neutral solution. The effect of acid on the zymogen 



