FAT METABOLISM 729 



as has been known for long, there is marked disturbance of fat metab- 

 olism. The table shows that this increase affects all types of lipoids in 

 proportion to the severity of the disease. 



Bloor considers that lecithin which is soluble in water, is the main 

 form in which fat is transported in the blood. The lecithin is taken up 

 by the tissue cells in which there are enzymes (esterases) capable of 

 hydrolysing it so as to produce fat, or by reversible action, of converting 

 the fat stored in the cells to lecithin which is then sent into the blood. 

 The fat secreted in the milk can, for example, all be accounted for by the 

 difference between the lecithin content of the blood plasma passing 

 through the gland (Meigs). Some of the fat is also transported in the 

 blood by the leucocytes acting as phagocytes towards it. 



The Destination of the Fat of the Blood. In general, it may be said 

 that the blood fat is transported to three places: (1) the depots for fat; (2) 

 the liver; and (3) the tissues. The fat present in each of these places 

 differs from that in the others, as is revealed by chemical examination 

 by the methods described on page 719. The depot fat usually yields about 

 95 per cent of its total weight as fatty acid. The tissue fat, on the other 

 hand, yields only about 60 per cent of its total weight as fatty acid. 

 This difference indicates that the fatty acid must be combined in the 

 tissues with a much larger molecule than is the case in the fat of the 

 depots. This large molecule is probably that of lecithin or other phos- 

 pholipin, and the smaller molecule in the depots, that of neutral fat. 

 The liver fat takes an intermediate position between depot fat and tissue 

 fat in its yield of fatty acid. When no active metabolism of fat is go- 

 ing on, the liver fat is like that of the tissues; but when fat metabolism 

 is active, the liver fat occupies an intermediate position between tissue 

 fat and depot fat. 



Another difference among the fats in these three places is with regard 

 to the degree of saturation of the fatty-acid radicles. This, it will be 

 remembered, is indicated by the iodine value; the higher the iodine 

 value, the greater the desaturation of fatty acid. In depot fat this value 

 is relatively low for example, about 30 in the goat and about 65 in man ; 

 depending somewhat on the fat taken in the food, compared with which 

 it is usually a little higher. The fat in the tissues, on the other hand, 

 has a high iodine value, possibly 110 to 130. The iodine value of the 

 fat of the liver is remarkably inconstant, being about the same as that 

 of the tissues when fatty-acid metabolism is not particularly active, but 

 approximating that of the depots when fat mobilization is proceeding. 

 The significance of this fact we shall consider later. 



