242 NUTRITION OF FARM ANIMALS 



resulting from the use of a certain feed or ration and approxi- 

 mately in what kind of material (protein, fat, gJycogen) the 

 energy lost or gained was contained/ The balance experiment, 

 therefore, is adapted to determine the total nutritive effect of 

 a given substance, while if the comparative slaughter test be 

 regarded as a form of balance experiment (284) the particular 

 organs or tissues in which gain or loss took place can be deter- 

 mined. 



The balance experiment, however, affords no insight into the 

 details of the chemical mechanism by which the observed nu- 

 tritive result is brought about. For example, balance experi- 

 ments have demonstrated that starch may serve as a source of 

 fat and have shown quantitatively the amount of fat formed 

 from a given weight of starch. As applied to known chemical 

 compounds, such a result as this is perfectly definite and of the 

 highest value, but it gives absolutely no information as to the 

 intermediate steps of fat formation, either in the processes of 

 digestion, resorption or metabolism. 



On the other hand, investigations of the intermediary metab- 

 olism, like those whose main results have been outlined in 

 Chapter V, have necessarily been to a large extent qualitative. 

 They have demonstrated some of the steps through which the 

 various anabolisms and katabolisms occur, but as a rule have 

 not attempted to deal directly with quantitative questions. 1 



Naturally the foregoing comparison is neither comprehensive nor 

 exclusive. It aims simply to point out a broad general distinction 

 between two types of nutrition investigation which in reality shade 

 into each other. 



Balance experiments have sometimes been characterized, 

 with a certain half contemptuous implication, as " bookkeeping 

 with the body." The characterization is a good one but the 

 implication is unwarranted. It is perfectly true, as some critics 

 of the balance experiment point out, that, for example, the most 

 accurate record of the income of raw materials and outgo of 

 finished products would of itself give a very incomplete notion 

 of the operations of a great factory and that the successful 

 conduct of such an enterprise requires as intimate a knowl- 



1 For a summary of some of the more important of these methods compare 

 Dakin, Oxidations and Reductions in the Animal Body, Chapter III. 



