64 



Feeds and Feeding. 



91. Liebig's theory.— It was held by Liebig that the exercise 

 of force is due to the breaking-down of lean-meat tissue in the 

 animal body, as is shown by the following :» 



"The amount of azotized food (protein) necessary to restore 

 the equilibrium between waste and supply is directly propor- 

 tional to the amount of tissues metamorphosed, 



"The amount of living matter, which in the body loses the 

 condition of life, is, in equal temperatures, directly proportional 

 to the mechanical effects produced in a given time. 



"The amount of tissue metamorphosed in a given time may be 

 measured by the quantity of nitrogen in the urine. 



" The sum of the mechanical effects produced in two individuals 

 in the same temperature is proportional to the amount of nitrogen 

 in their urine; whether the mechanical force has been employed 

 in voluntary or involuntary motions, whether it has been consumed 

 by limbs or by the heart and other viscera." 



92, Lawes and Gilbert's trial, — Lawes and Gilbert held a different 

 view, believing that protein did not play the exclusive part in the 

 production of energy claimed for it. Putting their doubts to test, 

 they conducted the following experiment: ^ Two pigs of similar 

 weight and appearance were selected. To one was given all 

 it would consume of lentU meal, a feed rich in protein, containing 

 about 4 per cent, of nitrogen. The other pig was fed all it would 

 consume of barley meal, containing less than 2 per cent, of nitro- 

 gen. Bach pig was confined in a frame, with arrangements for 

 collecting the faeces and urine separately. All the usual precau- 

 tions for good work were observed, with the following results: 



Feeding pigs protein-rich and protein-poor rations — Bothmnsted 



Station. 



» Organic Chemistry in its Application to Physiology and Pathology. 

 » Jour. Roy. Agl. Boc, 1895; Bui. 22, Office of Expt. Sta. 



