THE LIVER AND PANCREAS 245 



Bile cannot split up fats into fatty acids and glycerin, as the 

 pancreas does, but its presence increases threefold the action of 

 the pancreatic fluid in this respect. Once the fats are split, the 

 bile takes an active share, for fatty acids, which are insoluble 

 in water, are soluble in bile salts and lecithin, the latter greatly 

 increasing the power of the bile salts as fat solvents. The fatty 

 acid forms soaps with the alkali of the intestinal and pancreatic 

 secretion, and these are also dissolved by the bile acids. The 

 solution of soaps so formed makes the emulsifying effect of the 

 bile permanent and absorption of fat easier. In Voit's experi- 

 ments on dogs it was found that by cutting off the flow of bile 

 to the intestine the absorption of fat fell from 99 per cent, to 

 40 per cent. ; the solvent action of bile on fat is the chief digestive 

 function of this fluid, but in its action on fat it works in con- 

 junction with the pancreatic secretion. We shall see later (p. 256) 

 how the presence of bile increases the energy of the pancreatic 

 fluid in the emulsification of fat. Bile has no action on proteins. 

 According to Hofmeister, the bile of the ox, sheep, and horse 

 converts starch into sugar, while the bile of the pig and dog pos- 

 sesses no such power, or only to a limited extent. It has been 

 said that bile has an antiseptic influence on the intestinal contents, 

 protecting them from putrefaction and promoting peristalsis ; for 

 it has been found that when it is prevented from entering the 

 bowels, constipation and extreme foetor of the intestinal contents 

 result. Bile, however, is not a true antiseptic. The clay- 

 coloured faeces obtained in jaundice are probably due to the 

 presence of unac ted-on fat ; the fat encloses the proteids which 

 putrefy, hence the odour. The bile acts as a natural purgative, 

 and keeps up intestinal peristalsis ; by so doing it hurries the 

 food residues out of the system before they undergo putrefactive 

 decomposition. 



Glycogen. 



It is quite certain that the largest gland in the body must have 

 some other function than that of the secretion of a fluid of com- 

 paratively unimportant digestive power, and such is the case ; 

 the liver manufactures and stores up in its cells a peculiar sub- 

 stance known as glycogen or animal starch. Glycogen is spoken 

 of as a starch, though it differs from vegetable starch in many 

 important characteristics ; thus, it is soluble instead of insoluble 

 in cold water, and it is stained reddish-brown instead of blue by 

 iodine. Though glycogen may be detected in the liver substance 

 by the iodine test, it is now believed that it is not actually de- 

 posited in the cells, but held there in weak chemical combination ; 

 for it cannot readily be extracted from the liver by means of cold 

 water, whereas outside the body it is readily soluble in water. 



