142 NUTRITIONAL PHYSIOLOGY 



be offset and the less likely will be a wasteful overflow when 

 a storm follows a term of low water. The conversion of an 

 intermittent supply into a constant one is the function of 

 the mill-pond, and it is equally the service of the tissues 

 holding glycogen. 



While a relatively sudden rise of sugar in the circulation 

 may produce glycosuria, a slight chronic excess over the 

 normal may have an entirely different effect. If the diet 

 is supplying day by day a little more carbohydrate than 

 the body is oxidizing, the surplus may be transformed to 

 fat. The opinion that starchy and saccharin foods are 

 fattening has scientific support as well as common observa- 

 tion in its favor. Glycogen formation is limited and we 

 may suppose that fat-building takes place when the gly- 

 cogen reserve is at its maximum and still more sugar is 

 offering. An important advance was made in physiologic 

 knowledge when Liebig called attention to the fact that a 

 cow's milk contains an amount of fat utterly out of pro- 

 portion to the scanty supply furnished by the food of the 

 animal. It had been believed that no such transformation 

 could be accomplished by animal tissues, and that all fat 

 found in the body or in the secretions must have been re- 

 ceived as fat. Liebig fell into error when he stated that 

 the milk-fat had been made solely from proteins and not at 

 all from carbohydrates, but he had taken a notable step in 

 recognizing the possibility of changing one food-stuff into 

 another. Quantitative experiments soon showed that car- 

 bohydrates must be given a very prominent place among 

 fat-forming materials. 



The steps through which sugar is transformed into fat 

 are little understood. A comparison of the composition 

 of the two makes it evident that a great deal of oxygen has 

 to be removed in the reactions. This element is never set 

 free in animal metabolism; in the present instance it is 

 separated in the form of carbon dioxid. This is not merely 

 a theoretic consideration, but a condition which can be 

 demonstrated by experiments upon an animal rapidly 

 gaining fat. A wood-chuck, for example, when it is eating 



