MAINTENANCE THE ENERGY REQUIREMENTS 281 



not really but only apparently maintenance rations. It is perhaps 

 hardly correct to say that in these experiments growth was main- 

 tained at the expense of the fat of the tissues. A more exact state- 

 ment of the case would be that the increase of protein tissue and 

 water masked the loss of fat. Presumably this effect would be less 

 marked in more mature animals, in which the true maintenance and 

 the live weight maintenance would doubtless approach each other 

 closely when measured over long periods. 



373. Methods of determining the maintenance requirement. 



The most obvious method for determining the maintenance 

 requirement of an animal is the method of trial. It consists of 

 varying the amount of feed until constancy of live weight is 

 attained or until a balance experiment shows equilibrium be- 

 tween income and outgo of matter and energy. This method, 

 if extended over a considerable length of time, is particularly 

 adapted to the determination of the live weight maintenance. 

 When tested by the more refined method of the balance ex- 

 periment, however, such a ration will only rarely and by acci- 

 dent be found to be exactly a true maintenance ration. Usu- 

 ally there will be revealed more or less gain or loss by the body 

 for which a correction must be applied. 



A second method consists of a comparison, like that used in 

 a previous paragraph (364), to illustrate the determination of 

 net energy values, between the effects of two different amounts 

 of the same feeding stuff or ration upon the balance of energy. 

 Such a comparison not only affords the means of computing 

 the net energy value of the feed consumed but also serves to 

 determine the energy requirement of the animal. The results 

 in the case cited were as follows : 



TABLE 42. DETERMINATION or MAINTENANCE REQUIREMENT 



