2o6 SCIENCE PROGRESS 



diagram, reproduced below, in which the abscissae represent 

 real nitrogen intake and ordinates real nitrogen output. Let 

 OM ( = m) represent the nitrogen output on a nitrogen-free diet 

 of adequate calorific value, that is, the nitrogen minimum. 



If an ideal protein (biological value = lOo) is given in 

 gradually increasing amounts and is fully utilised, the nitrogen 

 excretion will be constant at ni until the intake rises higher 

 than that value. The point E where ME = OM will therefore 

 represent the point of nitrogen equilibrium, beyond which the 

 graph will follow the line E E» at an angle of 45° to the axis 

 for increasing intake. 



In the case of proteins of value less than 100, equilibrium 

 will not be attained on an intake equal to w, but at some higher 

 level represented by Ej. On all amounts less than this the 

 output will exceed the intake and the graph will follow the 

 line MEj. Whether this line is straight or curved will depend 

 on : 



(i) Indivisibility of the N requirements of the body. 



(2) Uniform economy with var3ang N intake. 



If these conditions hold ME will be straight and its equa- 

 tion will be 



y == m + X tan 6 



where y is the real output corresponding with any real intake 

 X less than ei. Thomas's formulae can be very simply expressed 

 in terms of 6 ; Formula B 



T^^, Urine N in N-free diet + faeces N + balance 



BV = 100 ^^r-^ ; — — ' 



N intake 



becomes 100 ^ ^ = 100 (i — tan 6) 



If the two above conditions do not obtain, the graph would 

 tend to be a curved line and the curvature would express the 

 fact that a certain fraction of the body's needs could be 

 satisfied by a smaller amount of this protein than would 

 correspond with the amount required to obtain equilibrium. 

 Turning to the actual experiments, in which the authors were 

 themselves the experimental subjects, we find them planned 

 and carried through with remarkable care and precision. The 

 paper should be read in its entirety by all interested in nutri- 

 tion, but a brief reference to the chief conclusions may be 

 made here. The minimum nitrogen expenditure by the urine 

 was found to be somewhat less than 0-038 to 0-035 gn^- per kilo. 



On taking a diet of carbohydrate and fat of adequate fuel 

 value the urinary nitrogen falls in a regular and orderly manner, 

 capable of simple mathematical expression, approaching a 

 minimum in fiveto seven days, and on resuming an ordinary nitro- 



