330 



PHYSIOLOGICAL REGULATIONS 



balance. Starting with 0.015 gm. X, kg. hr., they gave slightly more 

 on successive days until output was no longer greater than intake. 

 But meanwhile the nitrogen content of the body was being depleted ; 

 the deficit so obtained may or may not have been serious; and 

 acclimatization of output (as in fig. 160) may have been slow or 

 fast. Balance finally occurred at 0.028 gm. X. kg. hr. (C, fig. 161). 

 Hence in nitrogen exchange, the time factor is large, for weeks 

 may be required to establish stationary rates at one bodily content. 



OilOr 



To+al Ni+roaen |n+ake— qmYkg hr 



Fig. 161. Eate of total nitrogen output in relation to rate of total nitrogen intake. 

 Points of nitrogen balance, indicated by 1, fall on line D, equality. Solid circles 

 (curve C) dog II of Eubner ('02), cf. figure 159, fed meat only. Squares and solid 

 triangles. 3 dogs of Michaud ('09). Open circles and triangles, dog of Voit and 

 Korkunoff (1895) ; curve B (triangles) indicate exchanges when fat and carbohydrate 

 supplements are given in large amounts, the difference from curve A (circles) being 

 "protein sparing." Periods vary from 1 to 14 days at diverse points. 



Several ordinary criteria of balance may be satisfied at any of many 

 nitrogen contents, for approximate equality of intake with output 

 occurs in a great range of contents. Hence the emphasis is placed 

 on the minimal nitrogen tunwver, the "practical or physiological 

 minimum." This is distinct from output in deficits of nitrogen 

 ("experimental minimum''). Actually nitrogen intake is much 

 more variable than water intake; the range of approximate bal- 

 ances that can be forced to occur for water, do frequently occur for 

 nitrogen. In dogs there appear to be no measurements of volun- 



