CHAPTER III. 



DIGESTION, RESPIRATION AND CALORIMETEY. 



I. Digestibility of Feeding Stuffs. 



46. Variation in digestibility of feeding stuffs. The leading 

 quality of feeding stuffs is digestibility. Milk is practically all 

 digestible. Most of the nutrients in corn meal yield to the 

 digestive solvents, while rye straw is of such character that a 

 large portion of its substance is indigestible, and therefore inert 

 in the alimentary tract. In studying the digestibility of a given 

 feed, the chemist first determines by analysis the percentage of 

 each of the nutrients it contains. Weighed quantities of the 

 feed are then given to some animal and the solid excrement 

 voided during the trial is saved, weighed and samples of it 

 analyzed. Knowing how much of each nutrient was fed and 

 how much re-appears in the solid excrement, the difference is 

 held to be the portion digested, since it must have been retained 

 in the body. 



47. A digestion trial with sheep. As illustrating the manner 

 of conducting digestion trials, the following description is given 

 of one conducted by Armsby with sheep at the Wisconsin 

 Station. l Desiring to ascertain the digestibility of clover hay 

 and malt sprouts by sheep, two wethers weighing 87 pounds each 

 were selected for the trial. They were closely confined in 

 separate apartments specially constructed for the purpose, and 

 fed from zinc-lined feed boxes arranged to prevent the fodder 

 from being wasted. Each day's ration was carefully weighed 

 and samples reserved for analysis. The solid excrement as it 

 passed from the wethers was collected by means of rubber-lined 

 bags attached to the hind quarters of the animal by a light har- 

 ness. These bags were emptied every twenty-four hours and the 



1 Rept. 1884. 



