METABOLISM, NUTRITION AND DIETETICS 



all the nitrogen corresponding to the proteins of the last meal 

 to be eliminated. On the second day the quantity of urea sinks 

 abruptly ; then begins the true starvation period, during which 

 the daily output of urea remains constant or diminishes very 

 slowly until a short time before death, when it rapidly falls, 

 and soon ceases altogether. An increase in the excretion may 

 precede the final abrupt decline (premortal increase). This 

 seems to indicate the time at which all the available fat has been 

 used up, and after which protein is no longer ' spared ' by the 

 fat.* If the animal has little fat in its body to begin with,'?the 

 rise in the urea ex- 

 cretion takes place 

 even after the first 

 few days. So long 

 as the fat lasts 

 the rate at which 

 it is destroyed 

 as estimated from 

 the amount of car- 

 bon given off minus 

 the carbon corre- 

 sponding to the 

 broken - down pro- 

 teins remains very 

 nearly constant after 

 the first day. The 

 fat to a certain ex- 

 tent economizes the 

 proteins of the star- 

 ving body, but how- 

 ever much fat may 

 be present, a steady 

 waste of the tissue- 

 proteins goes on. If non-nitrogenous food in the form of 

 sugar is supplied to an otherwise starving animal, the pre- 

 mortal rise in the nitrogen excretion does not occur. By giving 

 a sufficient quantity of sugar, or of sugar and fat, but 

 practically no protein (so-called nitrogen starvation), the ex- 

 cretion of nitrogen may be reduced to one-third of its amount 

 when no food at all is given. This is true both in animals and 

 man. In this way the daily excretion of nitrogen in a man has 



* If the animal has been for some time on a diet containing an abun- 

 dance of proteins, several days may elapse before the constant excretion of 

 urea is reached ; if the previous diet has been poor in protein, the constant 

 starvation output may be at once established. 



342 



FIG. 185. EXCRETION OF UREA IN STARVATION. 

 A is a curve representing the quantity of 



urea 



excreted daily by a fat dog in a starvation period 

 of sixty days. B is the curve of urea excretion in 

 a lean young dog in a starvation period of twenty- 

 four days. Both are constructed from Falck's 

 numbers, but in A only every third day is put in, 

 in order to save space. The numbers along the 

 vertical axis represent grammes of urea ; those 

 along the horizontal axis days from the beginning 

 of starvation. 



