PART IV. 



PHYSIOLOGICAL CHEMISTRY (ADVANCED) 

 CHAPTER I. 



CARBOHYDRATES. 



Chemical Relationships. Although the ' hexoses ' are the sugars 

 of greatest physiological interest, it must be remembered that 

 * pentoses ' (wood sugars) do occur in the animal organism. They have 

 been separated from a nucleo-proteid obtained from the pancreas by 

 Hammarsten, and from yeast by Kossel. They differ from the hexoses 

 in that they do not ferment with yeast. When given by the mouth 

 they are excreted unchanged by the urine, indicating that they are not 

 assimilated by the organism. 



The Chemical Constitution of Sugars has recently been determined 

 by Emil Fischer, chiefly by studying the compounds formed with 

 phenyl-hydrazine. 



Place O'l gr. of dextrose in a test-tube, dissolve in water, and add 0*1 

 gr. phenyl-hydrazine hydrochloride and O2 gr. sodium acetate 

 crystals, warm gently till everything is dissolved, and then place for 

 half an hour in a boiling water bath. Allow to cool gradually, when a 

 yellow precipitate of osazone will separate out. Examine this under 

 the microscope, and notice that the precipitate is composed of needle- 

 shaped crystals arranged in rosettes or sheaves (Fig. 266). 



The chemical reaction takes place in two stages. 



Firstly, the < ' of the - CHO group of the sugar reacts with the ' H 2 ' of the 

 *NH 2 ' group of the phenyl-hydrazine to form H 2 0, the sugar and phenyl- 

 hydrazine combining to form Hydrazone. 



CH 2 OH(CHOH) 3 CHOH - CHiO ^iN - NH(C 6 H 5 ). 



Sugar, Phenyl-hydrazine. 



2 I) 



