180 THE PROCESSES OF DIGESTION AND RESORPTION. 



The fact that neither elastin nor collagen (gelatin) gives rise to 

 the formation of hetero-albumoses is of special interest in view of 

 the fact that both substances cannot be regarded as true food-stuffs, 

 viz., they are unable to maintain the nitrogenous equilibrium of the 

 higher animals when exclusively used. Whether or not this is due 

 to the absence of the aromatic group in the gelatin, and its presence 

 only in small amounts in elastin, is not decided. The hexon bases 

 are manifestly of no moment in this connection, as gelatin, at least, 

 yields rather more arginin than any of the common albuminous food- 

 stuffs, and, as I have pointed out, Ellinger has shown that the 

 hexon bases alone are likewise not capable of maintaining nitro- 

 genous equilibrium. Future researches, no doubt, will explain this 

 essential difference between the albumins proper, including the 

 proteids and the albuminoids. 



A digestion of other albuminoids, notably of the keratins, does 

 not take place in the small intestine of the higher animals, while 

 some of the invertebrates, such as the common house moth, are 

 manifestly capable of utilizing these also for purposes of nutrition. 

 In contradistinction to collagen and elastin, the keratins yield a 

 relatively large amount of ty rosin, in addition to leucin, aspara- 

 ginic acid, and glutaminic acid, on hydrolytic decomposition. 



DIGESTION OF THE FATS. 



Notwithstanding innumerable researches in this direction, our 

 knowledge of the digestion of fats and their subsequent absorption 

 is still imperfect. This is true more especially of the role which 

 the pancreatic juice and the bile play in the process. That both 

 secretions are actively concerned in the digestion of the fats can- 

 not be doubted. Minkowski and Abelmann have thus shown that 

 following extirpation of the pancreas in dogs the absorption of fats 

 ceases altogether, if we except the fat of butter, of which from 28 to 

 53 per cent, can still be utilized. Other observers, it is true, 

 obtained results which differ somewhat from those of Minkowski ; 

 but in all cases it could at least be^cjnonstrated_jthat hi the absence 

 of thejjajncreatice jml3l5^jt)sofpnon^^ IrToTher 

 experiments in which the bile was prevented from entering the 

 intestinal tract it was similarly demon s|rnfpfl thnt, only one-seventh 

 to one-half of the fat was resorbed, while the remainder, princi- 

 pally in the form of fatty acids, appeared in the feces.) This is the 

 more remarkable, since Munk has shown that the fatty acids can 

 be absorbed as such, and are retransformed into neutral fats in the 

 intestinal mucous membrane. 



While the importance of the pancreatic juice and the bile in the 

 digestion of the fats is thus manifest, \ve have no clear conception 

 of the manner in which their presence favors their resorption. It is 

 generally stated that this is primarly dependent upon a previous 

 emulsification, which is supposedly effected through the activity of 



