THE PRODUCTION VALUES OF FEEDING STUFFS 633 



or it might affect specifically certain more delicate parts of the 

 machine and so reduce the efficiency of the machine and cause it 

 to yield less finished product per unit of raw material consumed. 



In which of these two ways a deficiency in " accessory sub- 

 stances " affects the nutrition of an animal does not appear to 

 have been determined. It would seem probable, however, that, 

 in the case of a young animal, for example, a deficient dietary 

 acts to slow down or stop the whole group of anabolic processes 

 involved in growth. 1 The organs would thus be rendered in- 

 capable of converting a normal daily amount of feed into body 

 substances and a corresponding decrease in feed consumption 

 would presumably follow. In such a case it is quite conceivable 

 that such feed as was actually eaten in excess of the maintenance 

 requirement might be -just as efficient in producing gain and 

 have as great a production value per unit as in a normal ration. 

 In other words, it is conceivable that lack of the " accessory sub- 

 stances " may, in a sense, affect the economic rather than the 

 physiological efficiency of the ration. The writer has failed to 

 note any experiments in which this aspect of the matter has been 

 considered. In practically all reported investigations upon the 

 influence of " accessory substances," the feed consumption has 

 been regulated by the appetite of the animal and in many in- 

 stances has not even been reported. 



The undoubted importance of the accessory ingredients of 

 feeding stuffs has led, on the part of some writers, to a tendency 

 which as yet appears hardly justified to minimize the signifi- 

 cance of the production values in the older sense. The subject 

 is too new and the field too broad to warrant dogmatic con- 

 clusions, but it still remains true that the prime function of a 

 feeding stuff is to supply structural material and energy for 

 the body, and its potentialities in this respect are expressed in 

 its production values. That the results attained by its use 

 in practice are affected by other considerations has long been 

 recognized. Thus, if a feeding stuff is unpalatable for some 

 reason and is not eaten freely, the portion consumed may 

 show a high nutritive effect per unit and yet the use of the 

 feed be inadvisable. The presence of toxic substances might 



1 Naturally such an effect might be brought about by a retardation of certain 

 specific metabolisms upon which the whole growth process depended and the spe- 

 cific metabolisms affected might differ in different cases. 



