CHAPTER LXXVIII 

 FAT METABOLISM (Cont'd) 



THE FAT OF BLOOD 



Methods of Determination. Normally the blood contains only a small 

 percentage of fat, but after a fatty meal it may contain so large an 

 amount that the fat actually rises to the surface of the blood like a cream. 

 By means of the ultramicroscope, examination of the blood in the dark 

 field after a fat-rich meal reveals the presence of glancing particles, 

 the so-called "fat dust." These particles are most abundant about six 

 hours after the meal has been taken, and they gradually disappear by 

 the twelfth hour. They do not appear after a meal when the thoracic 

 duct is ligated. They disappear when oxygen is bubbled through the 

 blood. 



Fat dust has also been found abundantly present in the blood of em- 

 bryo guinea pigs at full time, but not in the mother's blood. This would 

 indicate that the placenta must have the power of taking the constitu- 

 ents of fat from the mother's blood and building them into fat, which 

 then passes into the blood of the fetus. The placenta under these condi- 

 tions acts like the mammary gland. In this connection it is of interest 

 that there is also much fat present in the blood of pregnant women. The 

 fat content of the placenta is, however, greater in the early stages of 

 pregnancy than later. 



Although these facts have been known for some time, it has been 

 impossible, either on account of the large quantities of blood required 

 for a chemical examination or because of the difficulty in estimating 

 the amount of fat from the density of the ' ' fat dust, ' ' to follow with any 

 great degree of accuracy the exact chemical changes that take place in 

 the fat of the blood. Recently, however, Bloor has succeeded in elab- 

 orating methods by which the fat content of the blood can be determined 

 with satisfactory accuracy in small quantities of blood, so that a con- 

 tinuous series of observations can be made over a considerable period. 



The fat is extracted from the blood by an alcohol-ether mixture with moderate heat. 

 An aliquot portion of the nitrate is evaporated in the presence of sodium ethylate, which 

 saponifies the fat. The residue, consisting of soap, is well washed and then treated 

 with hydrochloric acid so as to precipitate the fatty acid. The density of the precipitate 



696 



