NORMAL FAT METABOLISM 199 



fats. It also increases the formation of soaps from the fatty acids as 

 shown by Pfliiger, and later by Kingsbury. These effects are partly due 

 to the bile salts but to a considerable extent to other substances, e. g., mucin 

 and lecithin. 



The accelerating or activating effect of bile on the pancreatic lipase 

 has been shown by Eachford and by von Fiirth and Schiitz, who found 

 that the fat splitting power of pancreatic juice was increased several fold 

 by the presence of bile. The active substance in the bile which produces 

 the acceleration has been, shown by both investigators to be the bile 

 salts. Aside from any positive action of the bile the mere exclusion from 

 the intestine of a pint or more of alkaline colloidal secretion must have a 

 profound effect on intestinal processes. As regards further and unknown 

 functions of the bile mention should be made of the important findings of 

 Hooper and Whipple that dogs cannot long survive complete exclusion 

 of bile from the intestine unless liver is included in their diet. 



In the absence of both bile and pancreatic secretion very little fat is 

 absorbed, probably not over 20 per cent of emulsified fat, is in milk, 

 and much less of non-emulsified fat, although splitting is generally good 

 80 to 90 per cent of the rejected fat consisting of free fatty acids. Traces 

 only of soaps are present, which would point to the lack of alkali ordi- 

 narily furnished by the pancreatic secretion and the bile as the significant 

 factor in absorption. 



The Nature of the Food Fat. Lipase can act only on the surface of 

 the fat, hence the necessity as a preliminary step, of breaking up the 

 fat masses to as fine a state of division as possible as in emulsions, 

 so as to increase the available surface. For ready emulsification the fat 

 must be liquid or at least semi-solid at body temperature, and we find 

 that the utilization of a food fat depends largely on its fluidity at body 

 temperature. Thus v. Walther, in feeding experiments, found that various 

 fats which were liquid at body temperatures were absorbed to the extent 

 of 97 to 98 per cent, while tristearin (m.p. 60 C.) was absorbed to the 

 extent of only 14 per cent. Dissolving tristearin in almond oil so as to 

 bring the melting point down to 55 increased its absorption to 89 per 

 cent, indicating the importance of the liquid fats and especially of triolein 

 as a solvent for the harder fats, making it possible to deal with them in the 

 organism both in hydrolysis and in transport. On the other hand, experi- 

 ments with ethyl stearate (m.p. 30 C.) have shown that melting point in 

 the intestine is not the only factor in absorption, since this substance is 

 very little better absorbed than tristearin, although it is liquid at body 

 temperature. Also when it reaches the thoracic duct (as tristearin) it 

 was found mixed with enough softer fat to bring its melting point down 

 to near body temperature. It seems from these experiments that the 

 organism is able to protect itself against the absorption of high melting 

 fat which it would have difficulty in dealing with, first by limiting the 



