METABOLISM 307 



leaves in the form of sugar. It is held in storage in the 

 less soluble and more manageable forms of glycogen 

 and starch respectively. While glycogen is conspicuous 

 in the liver it is formed and retained by other tissues to 

 some extent. The skeletal muscles, in particular, con- 

 tain it in a small percentage but a large total quan- 

 tity. They constitute a mass of tissue many times larger 

 than the liver and they are supposed to contain rather 

 more glycogen than the great gland where it was first 

 found. 



Owing to the tendency of the liver and the muscles to 

 make glycogen when an excess of sugar is brought under 

 their influence and to return sugar to the circulation 

 when there is no influx from the intestine the blood is 

 protected against alternate surcharging and impoverish- 

 ment. Its sugar content does not rise materially unless 

 a great deal of sugar is fed. It is sometimes possible, 

 however, to exceed the capacity of the tissues for storing 

 glycogen and to establish for a short time a condition of 

 hyperglycemia, an abnormally high percentage of sugar 

 in the blood. If this is at all marked some sugar will 

 pass into the urine ; the kidneys will abstract it from the 

 blood if the liver and muscles fail to do so. The ap- 

 pearance of sugar in the urine in consequence of eating 

 largely of it is called alimentary glycosuria. 



If the carbohydrate supply of the body is for some 

 time in excess of the current consumption the formation 

 of glycogen will not be indefinitely continued. Instead, 

 there is likely to be a transformation of some of the 

 starch and sugar consumed into body fat. The maxi- 

 mum storage of glycogen is probably about 1 pound. 

 When this limit is approached conditions are favorable 

 for the development of more or less fat from carbohy- 

 drate. This possibility was once denied but has been 

 proved by careful experiments as well as by practical 

 experience. We have every reason to believe that 

 starches and sugars are responsible for much of the 

 corpulence which is such a common and serious condition. 



