FATS LECITHIN CHOLESTEROL. 103 



warm-blooded animals. Among the latter there are many differences, 

 depending on the species. For instance, human fat melts at about 25 C., 

 mutton-tallow at about 50 C., and fat of the horse at about 65 C. 



The fats decompose according to their composition, by taking on water, 

 into fatty acids and glycerol. This hydrolysis can be accomplished by 

 various agents, for instance by boiling with dilute mineral acids, or with 

 alkalies especially in the presence of alcohol, and, above all, by the action 

 of specific and widely distributed plant and animal ferments known in 

 this case as lipases. The process of decomposing fats is called saponifica- 

 tion. 1 If this be accomplished by the action of free bases, we do not 

 obtain free fatty acids, but their salts. These are called soaps. Although 

 the sodium and potassium soaps are easily soluble in water, the fatty acid 

 salts of the alkaline earths (calcium, barium, and magnesium soaps) are 

 insoluble. The neutral fats are perfectly insoluble in water. If we shake 

 them long and vigorously with water, we obtain an emulsion, which, how- 

 ever, soon disappears, while the fat separates again on the surface of the 

 water. Absolutely neutral fats, i.e., fats which do not contain a trace of 

 free fatty acid, cannot be emulsified even by shaking with dilute, alkaline- 

 carbonate solutions. When any free fatty acids are present, however, an 

 extremely fine, permanent emulsion is obtained. 



With few exceptions fats are of little influence in plant economy, 2 being 

 of far less importance than the carbohydrates. As a whole, they form 

 reserve material. In seeds, like Helianthus and Curcubita, we notice the 

 stored-up fat quickly disappears on germination. Concurrently we observe 

 an appearance of free fatty acid. A splitting of fat occurs, as was first 

 shown by Sigmund, 3 by the action of a specific ferment, lipase, also called 

 steapsin. More recently, extensive investigations have been made on 

 tEevery active lipase occurring in the seed of the castor-oil plant. 4 This 

 ferment is active in a weakly acid solution. The saponification of the fat 

 evidently changes it into such a condition that it can penetrate into the 

 protoplasm, and through the cell- walls. Small amounts of fatty acid in 

 the presence of alkali suffice to produce an emulsion. It has been demon- 

 strated experimentally that these extremely minute globules are capable 

 of penetrating the cell-membranes, although it has not been decided 

 definitely, how large a quantity of the neutral fat is saponified. Again, 

 nothing definite is known at present concerning the further behavior of 

 the fatty-acids, though Sachs has shown that their disappearance coin- 



1 J. Gad: Arch. Anat. Physiol. 1878, 179-187. 



3 Cf. F. Czapek: Biochemie d. Pflanzen, vol. i, pp. 115-126. Jena, 1905. 



3 W. Sigmund: Sitzungsber. d. Wiener Akad. 99, 407 (1890) ; 100, 328 (1891); 101, 

 549 (1892). 



4 W. Connstein, E. Hoyer, and H. Wartenberg: Ber. 35, 3988 (1902). Connstein: 

 Arch. Anat. Physiol. 1905. 



