TRANSFERENCE OF FOOD MATERIALS 135 



These chemical findings with the histological appearances 

 indicate that the fats pass into the cells as fatty acids (or soaps) 

 and glycerine. These unite to form neutral^fat, hence the 

 appearance of fat globules about the middle of the cell, although 

 the absorbing border is homogeneous. Even if fatty acids 

 are fed to an animal they are united with glycerine to form 

 neutral fats. The glycerine must be formed by the cells of 

 the body, probably from carbohydrate.* 



The digestibility and absorbability of fats depend upon 

 their melting point : the lower the melting point the more 

 complete is their digestion and absorption. A low melting 

 point is due either to fatty acids of low molecular weight or 

 to the presence of unsaturated linkages in the fatty acid 

 molecules. The soaps of the fatty acids and the acids them- 

 selves are more soluble the smaller the molecular weight and 

 the more unsaturated the acid. Hence the ease of absorption 

 seems to be related to the solubility and diffusibility of the 

 products formed from them. I The formation of insoluble 

 soaps such as the calcium soaps may be associated with 

 pathological conditions. { 



Butter and cod-liver oil may owe part of their value to the 

 solubility of their digested products. This solubility is due in 

 the former to the presence of fatty acids with low molecular 

 weight and in the latter to the presence of unsaturated acids. 

 The more soluble acids tend to hold the less soluble in solution 

 with them, a circumstance which offers great difficulty when 

 one attempts to separate mixtures of the fatty acids. 



Bloor has recently emphasised the fact that fats may be 

 altered during absorption. Fats of high melting point have 

 their melting point decreased and the converse by the time 

 that they reach the thoracic duct. He believes that this 

 alteration occurs in the wall of the intestine. Fats with very 

 low molecular weight pass mainly into the blood stream and 

 not into the lymphatics. 



Absorption of Carbohydrates and of Proteins. The absorption 

 of carbohydrates and of proteins is not so easy to follow. By 

 placing a canula in the thoracic duct and by collecting the 

 lymph it can be shown that comparatively little of these 

 substances pass into the lymph, hence the blood stream must 



* Royal Society Committee, Journ. of Physiol., 1919, vol. 52, p. 

 328. 



t I. Munk, Ergeb. d. Physiol., 1902, vol. i, part I, p. 322. 

 J O. T. Williams, Biochem. Journ., 1908, vol. 3, p. 391. 

 W. R. Bloor, Journ. Biol. Chcm., 1914, vol. 16, p. 517. 



