LECTURE V. 



CARBOHYDRATES. 

 IV. 



BUILDING UP AND BREAKING DOWN OF CARBOHYDRATES IN THE 

 ANIMAL ORGANISM. 



WE found in the last lecture that the blood under varying physiological 

 conditions always maintained a constant sugar-content. This does not 

 increase when the food is rich in carbohydrates, nor decrease materially 

 during starvation. This phenomenon is explicable only by the assumption 

 that there is an extraordinarily delicate regulating mechanism which 

 works on the one hand in conjunction with the organs containing the 

 stored-up sugar, and on the other hand with the places where sugar is 

 consumed. If for any reason the amount of sugar in the blood increases 

 above the normal, then sugar appears in the urine. This may take place, 

 for example, when an excessive amount of sugar has been introduced into 

 the alimentary canal. In such a case it is not always possible to remove 

 the sugar fast enough from the general metabolism by converting it into 

 glycogen or fat. This ability of storing up sugar is a restricted one. 1 

 The maximum amount of sugar which it is possible for the system to 

 assimilate is known as the limit of assimilation, and the elimination of 

 sugar which takes place when this is exceeded is spoken of as alimentary 

 glucosuria. The limit varies with different forms of sugar and for different 

 individuals. In general, the danger of giving the blood an over-supply of 

 sugar under normal conditions of nourishment is but slight, because under 

 normal conditions the bulk of the carbohydrates are taken into the system 

 either as starch or as cane-sugar. There is no danger of these forms of 

 sugar being suddenly broken down in the alimentary canal; on the con- 

 trary, their decomposition always takes place gradually from one stage to 

 another so that this in itself serves in a measure to regulate the absorption 

 of sugar. 



Under certain conditions the assimilation limit for carbohydrates can 

 be reduced greatly for a time. This is particularly true of the central 

 organ of carbohydrate metabolism, namely the liver. Claude Bernard 3 

 recognized the fact that the storing up of sugar in the form of glycogen 



1 Cf. Franz Hofmeister: Arch. exp. Path. Pharm. 25, 240 (1889). 

 ' Legons (Cours du semestre d'hiver), 1854-55, p. 289. 



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