112 LECTURE VI. 



fat assimilation, we cannot get an exact explanation of the causes of 

 obesity. We are confronted by a condition which leads to many secondary 

 symptoms; above all we have to remember that a very large amount of 

 tissue has to be supplied with blood so that unusual strains are placed 

 upon the heart. The condition of those afflicted with obesity undoubtedly 

 depends upon their ability to satisfy these demands. 



The functions of fats in the animal organism are not restricted to the 

 part that they play as direct or indirect nourishment. In the growing 

 individual the fat which is in the cells, and also otherwise distributed in 

 the true fatty tissues, and the substances which are closely related to it, 

 play a part the importance of which we cannot yet fully estimate. We 

 are acquainted with many materials which are absorbed in a water-soluble 

 condition, and in this form they penetrate the cells. On the other hand, 

 we also know of many substances which are entirely insoluble in water, 

 but which are, nevertheless, easily taken up. The fats may in these 

 instances act as solvents. Although a substance is soluble in water, it 

 may be more so in oils; and this property may exert an influence on cellular 

 assimilation, and permit the cell to exercise a selection according to its 

 constitution and condition. This suggestion has been made by H. 

 Meyer * and by Overton 2 to explain the action of certain narcotics. It is 

 possible, and in fact, even probable, that such relations are important for 

 cell-metabolism, under ordinary circumstances. 



Closely related to the fats, and the functions which we have just con- 

 sidered, is the lecithin group. These, also, are combinations of glycerol 

 with fatty acids. Here only two hydroxyls are substituted by fatty acids 

 in the tri-atomic glycerol, while the third is replaced by a phosphoric acid 

 molecule which is also combined with the base, choline. The following 

 formula gives an idea of the constitution of lecithin, also called distearyl- 

 lecithin : 3 



CH 2 C 18 H 35 01 



AH- 



Glycerol radical 



Choline radical |N= (CH 3 ) 3 

 X OH 



C 18 H 35 



Fatty acid radical. 



CH 2 -0 , 



HO PO / Phosphoric acid radical. 



1 Arch. exp. Path. Pharm. 42, 109 (1899). 



2 Studien u. d. Narkose, etc., Jena, 1901. Cf. also H. J. Hamburger: Osmotischer 

 Druck u. lonenlehre in d. Medicin. Wiesbaden, J. F. Bergmann, 1904, vol. iii, 242. 



3 Cf. Diakonow: Zent. med. Wissensch. 1868, 438. F. Hundeshagen: J. pr. Med. 28, 

 219 (1883). E. Gilson: Z. physiol. Chem. 12, 585 (1888). A. Strecker: Ann. 148, 77 

 (1868). 



