FATS 197 



Between these forms there is an important histological 

 difference. The fats which are visible to the naked eye, 

 or are visible in globular form through the microscope, and 

 stain with the usual reagents are the triglycerides. They are 

 the fats of ordinary adipose tissue. The complex fats, such 

 as lecithin, are not visible microscopically, do not stain 

 in the usual way, but under certain pathological conditions 

 glycerides may separate out from the complex fats, and 

 form globules which stain in the characteristic manner. 



It is sometimes necessary to find out in any tissue how 

 much of the hpoid substance exists as triglyceride and 

 how much in the complex form. This is done by estimating 

 the proportion of fatty acid to the total hpoid. Comparison 

 of the formulae given above for glycerine tripalmitate and 

 for lecithin shows that the fatty acid constituent accounts 

 in the former for about 95 per cent, and in the latter for 

 about 60 per cent, of the whole molecule. 



Absorption of Fat 



Fat exists in blood in the form of ultra-microscopic 

 particles — the blood-dust. Its amount is increased after a 

 fat-rich meal. The greater part of the fat enters the blood 

 through the lacteals and thoracic duct. When the thoracic 

 duct is Hgatured, fat continues to leave the intestine, 

 though no demonstrable increase can be found in the 

 systemic circulation. The fat is evidently transported 

 from the intestine and deposited elsewhere with great 

 rapidity. The site of such deposit appears to be the liver, 

 for when fat absorption is in progress the fat in the portal 

 vein exceeds that in the jugular vein. 



In spite of the appearance of fat droplets within the 

 intestinal epithehum, there is overwhelming evidence to 

 show that fat is only absorbed after saponification into 

 soaps and glycerine, and that these, after passing through 

 the epithehum, are resynthesised. The evidence in favour 

 of this view is as follows : — 



