4 63 A MANUAL OF PHYSIOLOGY 



for all the nitrogen corresponding to the proteids 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 (pre-mortal 

 increase). This seems to indicate the time at which all the 

 available fat has been used up, and after which proteid 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 destroyed as estimated from the 

 amount of carbon given off minus the carbon corresponding 



A is a curve representing 

 the quantity of urea excreted 

 daily by a fat dog in a star- 

 vation period of sixty days. 

 B is the curve of urea ex- 

 cretion 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 hori- 

 zontal axis days from the 

 beginning of starvation. 



Fio. 136. EXCRETION OF URF.A IN STARVATION. 



to the broken-down proteids remains very nearly constant 

 after the first day. The fat to a certain extent economizes 

 the proteids of the starving body, but however much fat may 

 be present, a steady waste of the tissue-proteids goes on. 



The results obtained on fasting men differ in some respects 

 from those obtained on starving animals. In ten days of 

 hunger, Cetti, a professional ' fasting man ' of meagre habit, 

 excreted 112 grammes nitrogen, or an average of n grammes 

 a day. The excretion was least on the eighth, ninth, and 

 tenth days, namely, about 9 grammes a day. On the third 

 day it was higher than on the second, and almost as high on 



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

 ance of proteids, several days may elapse before the constant excretion 

 of urea is reached ; if the previous diet has been poor in proteid, the con- 

 stant starvation output may be at once established. 



