592 METABOLISM, NUTRITION AND DIETETICS 



For the first day of starvation the excretion of urea in a dog or 

 cat is not diminished; it takes about twenty- four hours for all the 

 nitrogen corresponding to the proteins of the last meal to be elimin- 

 ated. 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 (pre- 

 mortal 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 excretion takes place even after the 

 first few days. So long as the fat lasts the rate at which it is 



Fig. 199- Diagram showing Loss of Weight of the Organs in Starvation. The 

 numbers under I. are the percentages of the total loss of body-weight borne by 

 the various organs and tissues. The numbers under II. give the percentage loss 

 of weight of each organ calculated on its original weight as indicated by com- 

 parison with the organs of a similar animal killed in good condition. 



destroyed as estimated from the amount of carbon given off minus 

 the carbon corresponding to the broken-down proteins remains 

 very nearly constant after the first day. The fat to a certain extent 

 economizes the proteins of the starving body, but however 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 other- 

 wise starving animal, the premortal 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 starva- 

 tion), the excretion of nitrogen may be reduced to one-third of its 

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

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

 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 star- 

 vation output may be at once established. 



