PROBLEMS IN ANIMAL NUTRITION. 515 



a definite siibstanco, l)ii( on the other hand it will be a long time before 

 a sufficient ninnber of results of this sort are arcuniulated to furnish 

 a suflicient basis for a science of feeding. 



Finally, at least mention should be made of the importance of re- 

 search upon the influence of condiments; that is, of the various flavor- 

 ing and aromatic substances contained in feeding stuff's — what the 

 (lei-nians call IJeizstoffe, which might be translated '' stimulants," 

 were it not for the unfoi'tunate connotation of that word. We know 

 thai thc^c substances exert an important influence upon the nutritive 

 pi'ocesses in the animal. ]>ut beyond this our knowledge is vague and 

 ([ualitative. 



The Hues of investigation thus far suggested have to do with the 

 ivlativc values of feeding stuffs. The general applicability of any 

 such results, however, has been questioned because of varying indi- 

 viduality in animals. That such variations, and striking ones, do 

 exist is undeniable. Tt is not difficult, however, to suggest plausible* 

 explanations foi- them other than differences in the physiological util- 

 ization of the nutrients digested. For example, if of two animals one 

 has a maintenance recpiirement five per cent greater than the other, 

 due perhaps to greater I'estlessness of disposition, the quieter animal 

 will do better than the more restless one npon a given ration, not be- 

 caus' it uses its food physiologically to better advantage, but simply 

 because it has more left for ]>roductive purposes after meeting the 

 needs of maintenance. So too. if of two aninuils otherwise identical, 

 one is able to consume continuously ten per cent more food than the 

 other, it is obvious that a correspondingly larger proportion of its 

 food is available for productive purposes, since the same amount must 

 l)(^ subtracted for maintenance in both cases. I instance these simply 

 as ]:)ossible explanations without intending to assert that they or 

 similar ones are sufficient to account for all the observed difference. 

 The point is that the question is one needing investigation. 



In the first place, the maintenance requirements of different species 

 of animals, and their variation both as to proteids and total food, 

 should be more fully investigated. At the present time, only the data 

 for cattle can be regarded as fairly satisfactory. Such results are 

 indispensable for the rational study of the results of practical feed- 

 ing experiments. The influence of such factors as breed, individuality, 

 age. Aveight, and condition on the maintenance requirement should be 

 examined, as well as such external factors as the influence of the sur- 

 rounding temperature and of the greater or less incidental activity of 

 the animal. By careful methods much valuable information regard- 

 ing the actual maintenance requirement of animals may be gathered 

 l)y a combination of live weight and digestion experiments. AVhen, 

 however, we come to ask whether the maintenance value of a given 

 feeding stuff, or in other words, the net availability of its energy. 



