500 



DIGESTION IN THE INTESTINES 



[CH. XXXII. 



tion should be more accurately iiamed a-amiuo-isobutylacetic acid 

 (CH 3 ) 2 CH.CH ? .CH(NH 2 )COOH. 



Tyrosine is a little more complicated, as it is not only an amino- 

 acid, but also contains an - aromatic radicle. Propionic acid has the 

 formula C 2 H 5 .COOH ; amino-propionic acid is C 2 H 4 .NH 2 .COOH, and 

 is called alanine. If another H in this is replaced by oxyphenyl 

 (C 6 H 4 .OH), we get C 2 H 3 .NH 2 .C H 4 OH.COOH, which is oxyphenyl- 



FIG. 400. Crystals of leucine and tyrosine. x 216. 



amino-propionic acid, or tyrosine. Leucine and tyrosine are both 

 crystalline ; the former crystallises in the form of spheroidal clumps 

 of crystals, the latter in collections of fine silken needles (fig. 400). 



Polypeptides. E. Fischer has shown that in the cleavage of the proteid 

 molecule an intermediate stage in the formation of individual animo-acids is that 

 of the polypeptides, which are conjugated groups of such acids. Thus, he has 

 separated out, among others, leucyl-leucine, glyeyl-leucine, glycyl-asparagine, 

 alanyl-glycyl-leucine. He has also succeeded in making some of these syntheti- 

 cally, and so there is some promise in the future of a synthesis of the proteid 

 molecule itself. 



Extirpation of the Pancreas. 



Complete removal of the pancreas in animals and diseases of the 

 pancreas in man produce a condition of diabetes, in addition to the 

 loss of pancreatic action in the intestines. Grafting the pancreas 

 from another animal into the abdomen of the animal from which the 

 pancreas has been removed relieves the diabetic condition. 



How the pancreas acts other than in producing the pancreatic 

 juice is not known. It must, however, have other functions related 

 to the general metabolic phenomena of the body, which are disturbed 

 by removal or disease of the gland. This is an illustration of a 

 universal truth viz., that each part of the body does not merely do 

 its own special work, but is concerned in the great cycle of changes 

 which is called general metabolism. Interference with any organ 



