446 THE HUMAN BODY 



out exceeding the assimilation limit. Milk -sugar is split very 

 rapidly by its enzym, lactase, and its assimilation limit is corre- 

 spondingly low. Starch is digested so slowly that the assimila- 

 tion limit for it is quite difficult to exceed. Glycosuria resulting, 

 not from disease, but merely from overconsumption of carbo- 

 hydrates, is called alimentary glycosuria. 



Diabetes. When there is excretion of sugar from the kidney 

 because of disease, the condition is called diabetes. An analysis 

 of the carbohydrate-storage mechanism just described reveals 

 three points where an upset of the normal sequence might give 

 rise to glycosuria; and three corresponding varieties of diabetes 

 are known. The three conditions which may cause glycosuria are: 

 (1) A disturbance of the mechanism which controls the rate of 

 conversion of liver-glycogen into sugar, so that more is poured 

 into the blood than the tissues are able to use; (2) a diminution 

 in the consumption of sugar by the tissues, so that more accumu- 

 lates than the liver can store ; (3) an alteration of the kidney such 

 that it excretes all the sugar that comes to it, and thus drains 

 sugar from the blood continuously. Much insight into the work- 

 ing of the carbohydrate-storing mechanism, as well as the use of 

 carbohydrates by the Body, has been gained by study of these 

 three forms of diabetes. 



Diabetes from Disturbance of the Liver Function. It has been 

 shown that injury to a definite point in the medulla destroys the 

 coordination between the output of sugar from the liver and the 

 use of sugar by the tissues, with resulting glycosuria. This sug- 

 gests, of course, that the liver carries on its function of storing 

 and delivering sugar under the control of a reflex "center." Such 

 a method of control seems reasonable inasmuch as increased ac- 

 tivity of the tissues involves increased consumption of sugar, 

 with a greater call upon the liver for supplies, and, as we know, 

 the tissues most involved, the muscles, send into the medulla 

 streams of afferent impulses whenever they are active, which 

 would serve to excite the center. In corroboration of this idea it 

 may be stated that certain diseases of the central nervous system 

 in man result in an upset of the liver function of precisely this 

 sort. It must be admitted, however, that more evidence is re- 

 quired before the reflex control of the liver's storage function can 

 be said to be wholly demonstrated. 



