FAT METABOLISM 697 



thus produced is compared in an optical apparatus, called a nephelometer, with a 

 standard solution of two milligrams of oleic acid treated in the same way. The fatty 

 acids in human blood are mainly oleic and palmitic. 



The lecithin and cholesterol may also be estimated in the same blood extract. For 

 lecithin the above extract of blood, after the removal of the alcohol and ether, is digested 

 by heating with concentrated HNO 3 and H 2 SO 4 . This decomposes the lecithin, liberating 

 the phosphorus, a solution of the resulting ash being rendered faintly alkaline to phenol- 

 phthalein and then slowly added to a silver nitrate solution. The density of the pre- 

 cipitate thus produced is compared in the nephelometer with that of a precipitate pro- 

 duced in the same amount of silver nitrate by adding to it a standard phosphoric acid 

 solution. 



For cholesterol an aliquot portion of the above extract is saponified with sodium 

 ethylate and then saturated with chloroform ; the chloroform extract is mixed with acetic 

 anhydrid and H 2 SO 4 (con.) until the bluish color is fully developed (Liebermann reac- 

 tion), the intensity of which is then compared in a colorimeter with that obtained by 

 similar treatment from a standard cholesterol solution. 



Variations in Blood Fat. In the dog the percentage of fat in the 

 blood is remarkably constant under normal conditions. After a fatty 

 meal the increase in fat begins in about an hour, and reaches its maxi- 

 mum in about six. The increase is not found in animals in which the 

 thoracic duct has been li gated. Although this result would seem to 

 contradict the view held by some that part of the fat which can not be 

 accounted for in the thoracic-duct lymph 'is absorbed by way of the 

 portal vein, it does not by itself disprove the hypothesis, for it has been 

 found that the fat content of the portal blood is always higher than that 

 of the jugular. 



Very interesting results have been obtained following the intravenous 

 injection of emulsions of oil, either the so-called casein emulsion or col- 

 loidal suspensions. Up to a dose of 0.4 gram per kilogram of body 

 weight which by calculation would suffice to raise the fat content of 

 the blood by 100 per cent there was no increase in fat content. In or- 

 der to explain this disappearance of fat, it might be imagined that the 

 injected fat particles formed emboli in the smaller Capillaries. Against 

 such a view, however, is the fact that the particles of fat in these emul- 

 sions are one-half to one-seventh the size of a red corpuscle. Although 

 this argument is no doubt of some weight, it should be remembered 

 that the physical condition of these fine fat globules is not the same as 

 that of the red blood corpuscle. Their surface condition may be such 

 that they readily agglutinate so as to form small masses, which may 

 stick at the branching of the smaller arterioles and capillaries. Bloor 

 himself suggests that the injected fat may be stored, possibly in the liver, 

 since the fat in this organ, as we shall see later, increases under similar 

 conditions. When twice the above quantity was fed in the form of egg- 



