594 GENERAL METABOLISM [CH. XXXIX. 



Compare this table with that at the bottom of p. 589. 



Diabetes mellitus. In addition to the presence of sugar in the 

 urine in this disease, the most marked symptoms are intense thirst 

 and ravenous hunger. As a rule, diabetic patients digest their food 

 well. The thirst is an indication of the necessity of replacing the 

 large quantities of water lost by the kidneys; the hunger, that of 

 replacing the great waste of tissues that occurs. For not only does 

 the urine contain sugar, but, in addition, a great excess of urea and 

 uric acid. The carbonic acid output is somewhat smaller than in 

 health. In health the carbohydrates, after assimilation, give rise, 

 by oxidation, to carbonic acid ; in diabetes, all the carbohydrates do 

 not undergo this change, but pass as sugar into the urine. Not that 

 all the sugar of the urine is derived from carbohydrates, for many 

 diabetics continue to pass large quantities when all carbohydrate food 

 is withheld ; under these circumstances, it must be derived from the 

 destruction of proteid matter (see also pp. 516, 571). The increased 

 production of organic acids which lessen the alkalinity of the blood 

 should also be remembered (see pp. 518, 559). 



Luxus Consumption. 



In former portions of this book we have insisted on the fact that 

 the food does not undergo combustion, or katabolic changes, until 

 after it is assimilated, that is, until after it has become an integral 

 part of the tissues. Formerly the blood was supposed to be the 

 seat of oxidation ; but the reasons why this view is not held now 

 have been already given. When a student is first confronted with 

 balance-sheets, representing metabolic exchanges, it is at first a little 

 difficult for him to grasp the fact, that although the amount of 

 nitrogen and carbon ingested is equal to the amount of the same 

 elements which are eliminated, yet the eliminated carbon and hydrogen 

 are not derived from the food direct, but from the tissues already 

 formed; the food becomes assimilated and takes the place of the 

 tissues thus disintegrated. Let us suppose we have a tube open at 

 both ends and filled with a row of marbles ; if an extra marble is 

 pushed in at one end, a marble falls out at the other ; if two marbles 

 are introduced instead of one, there is an output of two at the other 

 end ; if a dozen, or any larger number be substituted, there is always 

 a corresponding exit of the same number at the other end of the tube. 

 This very rough illustration may perhaps assist in the comprehension 

 of the metabolic exchanges. 



The difficulty just alluded to, which a student feels, was also felt 

 by the physiologists who first studied metabolism ; and Voit formu- 

 lated a theory, of which the following is the gist : All proteid taken 

 into the alimentary canal appears to affect proteid metabolism in two 



