88 DISACCHARIDES, POLYSACCHARIDE8 AND GLUCOSIDES 



Glycogen is also found in glandular, epithelial and connective tissues 

 and in the brain. The distribution of glycogen in the body is very 

 variable; the following figures were obtained by Schondorff, employing 

 dogs which had been well fed with carbohydrates and meat shortly 

 before death : 



One hundred grammes of glycogen were distributed in different 

 parts of the body in the following proportion in seven dogs employed : 



Minimum Minimum 



observed. observed. Average. 



Blood 0.04 0.001 0.015 



Liver 56.74 20.09 37.97 



Muscle 62.55 31.22 44.23 



Bone . 12.88 5.36 9.25 



Skin 11.38 1.42 4.49 



Viscera 7.30 0.38 3.81 



Heart 0.28 0.08 0.17 



Brain 0.23 0.04 0.09 



It will be observed that the heart-muscle, which is in continual 

 activity, contains very little reserve-stock of carbohydrates. It is 

 evidently unable to accumulate a reserve or capital of carbohydrate 

 and maintains its activity upon its current income. With this may be 

 correlated the fact that after each beat of the heart a definite and 

 relatively lengthy period occurs, the "refractory period" during which 

 even the application of stimuli fails to elicit a contraction from the 

 heart-muscle, whereas ordinary striated muscle, containing abundant 

 stores of reserve carbohydrate, may be stimulated repeatedly at exceed- 

 ingly brief intervals until relaxation between the contractions becomes 

 a mechanical impossibility, and the contractions fuse into one "tetanic" 

 contraction which relaxes only when the muscle becomes exhausted 

 and its stores of glycogen depleted. 



It will be noted, also, that the percentage of glycogen in the blood 

 is extraordinarily low. In fact it appears that the only form in which 

 carbohydrate material circulates in the Vertebrata is that of glucose, 

 and that this is also the only form in which carbohydrate food is 

 utilized by the tissues for the production of energy, or the manufacture 

 of reserve-materials. Now the carbohydrates of the food are usually 

 ingested in the form of starch, glycogen, and other polysaccharides, or 

 in the form of disaccharides, such as cane-sugar or lactose, and these 

 carbohydrates are readily utilized by the organism. Preparatory to 

 utilization therefore, these carbohydrates must undergo elaborations 

 and transformations resulting in the formation of glucose. 



AMINO -POLYSACCHARIDES. 



The hydrolysis of proteins which contain a glucosamin radical yields 

 in some instances an amino-disaccharide, presumably diglucosamin. 

 The most important amino-polysaccharide in the animal economy is, 

 however, Chitin, which forms the exoskeleton of the Jnsecta and the 



