DIGESTION AND RESORPTION 



less proportion of excretory products (154). In the case 

 herbiyora, the proportion of the latter is relatively small and 

 in the digestion experiment as ordinarily conducted is neglected, 

 it being assumed, in other words, that the feces are equivalent 

 to undigested feed residues. The same method is pursued in 

 digestion experiments with swine, although in these animals -- 

 the proportion of excretory products in the feces is larger. The 

 error thus introduced into digestion experiments is not negligible, 

 especially as regards certain ingredients. It will be convenient, 

 however, to take up first the methods of digestion experiments 

 as ordinarily conducted and to consider later the nature and 

 extent of the errors introduced by neglecting the presence of the 

 excretory products. 



159. Time required for digestion experiments. It is es- 

 sential that a digestion experiment be preceded by a prelimi- 



FIG. 15. Steer in digestion stall. (Bailey's Cyclopedia of American Agriculture.) 



nary period in which the feed to be investigated is fed in the same 

 weighed amounts daily as in the actual experiment. This is 

 for the purpose of removing from the digestive tract residues 



