METABOLISM 313 



from corn to meet the needs of the system we are not to 

 conclude that corn is a poor food. It may be one of the 

 best possible to mix with some other which will give quite 

 different percentages of the amino-acids. Moreover, if 

 we admit financial considerations it will be necessary to 

 bear in mind that much more of the cereal proteins can 

 be had for a dollar than of those in meat, milk, and eggs. 



Urea. We usually eat much more protein than is 

 absolutely necessary. Even if we do not, there are bound 

 to be amino-acids in the circulation for which there is 

 no present demand. These are not wasted altogether. 

 The nitrogen which they contain is withdrawn from their 

 molecules, not as an element but in the compound urea. 

 This is a soluble, non-irritating compound which is 

 excellently adapted to be the chief nitrogeneous excretory 

 product. Much of it is formed in the liver, but much is 

 also manufactured in the tissues at large. It circulates 

 until removed from the blood by the kidneys. 



After the formation of urea has been accomplished the 

 residue of the amino-acid molecules seems to have a 

 history identical with that of carbohydrate in the 

 metabolism. In fact a considerable part of the proteins 

 we eat seems to exist later as sugar. Hence there is a 

 possibility of glycogen formation from protein and, as 

 previously suggested, possible transformation into fat 

 of some of the protein sugar. In diabetes the sugar 

 formed from protein comes to light and makes its ap- 

 pearance even in fasting when the proteins of the body 

 are being consumed. It will be realized that a diabetic 

 suffers not only from the loss of the power to utilize 

 carbohydrates, but is deprived to a great extent of the 

 support of protein. When, at the last, he can no longer 

 oxidize fat successfully the problem of his nutrition is 

 hopeless. 



To work over the amino-acids in such a way as to sepa- 

 rate urea from them and then to turn the remainder into 

 dextrose may seem a roundabout and costly mode of 

 getting sugar. This is a fair argument against the over- 



