VARIABLE AND CONSTANT COMPONENTS 



599 



et a/., 384 in their original work, to state that "In its lipid distribution, the 

 liver of the fasted mouse is like the normal liver." 



In their later investigations, MacLachlan and his collaborators 353 dem- 

 onstrated that a remarkable change in the composition of phospholipids 

 takes place during this interval of fasting. Whereas the proportion of 

 a-lecithin and /3-cephalin was decreased by as much as 80%, that of 0- 

 lecithin and a-cephalin remained constant, or was actually slightly increased 

 over this period. This results in a seemingly constant lecithin :cephalin 

 ratio, in spite of the marked qualitative variations. These changes are 

 summarized in Table 19. 



Table 19 



The Distribution of Phospholipids in the Livers of Unfasted Mice, and of 



Mice Fasted for 1 to 4 Days' 1 



Number of days of fasting 

 Category 12 3 4 



Initial wt., g 20 4 20.7 21.1 21.0 20.8 



Carcass wt., g. 6 18.30 16.50 15.08 13.65 12.70 



Liver wt., g 1.265 1.076 0.957 0.803 0.648 



Liver /g. mouse, mg 65 62 60 56 49 



Total lipids, mg 66 107 110 42 20 



Total phospholipid, mg 41 33 30 25 18 



Phospholipid fractionation 



a-Lecithin, mg. and(%).. 12.2(34) 8.0(26) 7.3(25) 5.4(21) 3.6(16) 

 ^-Lecithin, mg. and (%). . 7.2(20) 10.0(32) 9.2(31) 8.8(34) 8.1(35) 

 a-Cephalin, m^.and(%).. 7.0(19) 7.8(25) 7.2(24) 8.5(32) 8.8(39) 

 0-Cephalin, mg. and(%).. 9.7(27) 5.4(17) 5.9(20) 3.4(13) 2.4(10) 

 Total lecithin, % phospho- 

 lipid 58 57 57 56 55 



Phospholipid, % liver wt. d . . 3.24 3.07 3.14 3.12 2.79 



Total lecithin : total cephahV 1.16 1.36 1.26 1.19 1.04 



a Adapted from P. L. MacLachlan, H. C. Hodge, W. R. Bloor, E. A. Welch, F. L. 

 Truax, and J. D. Taylor, /. Biol. Chem., 143, 473-490 (1942). 

 6 Carcass, not including liver weight. 



c Including per cent of total phospholipid (in parentheses). 

 d Calculations by present author. 



Thus, it has been suggested that a-lecithin and /3-cephalin might be de- 

 scribed as "metabolic" phospholipids which presumably owe their normal 

 existence to the ordinary lipid metabolism of the liver. Such compounds 

 may likewise be considered as "labile" phospholipids, which can be utilized 

 during an emergency such as inanition. This concept, that two types of 



364 H. C. Hodge, P. L. MacLachlan, W. R. Bloor, C. A. Stoneburg, M. C. Oleaon, and 

 R. Whitehead, J. Biol. Chem., 139, 897-915 (1941). 



