130 THE CHEMISTRY OF CATTLE FEEDING 



the former figure as the fundamental unit, and assuming the 

 same relative variation as before, the formula to be used in 

 calculating maintenance rations for sheep of different size 

 would be 



log E = 07 log M o'8 



Respiration Chamber Experiments. Much valuable in- 

 formation regarding the quantities of food required by animals 

 under different conditions was derived from the older experi- 

 ments. In these' the plan generally followed was the simple 

 and obvious one of feeding the animals on food of known 

 composition. The food was, of course, accurately weighed, 

 and the quantities were varied until the desired effect was 

 produced according to the purpose of the experiment. The 

 effects were determined by weighing the animals from time to 

 time. 



The knowledge so obtained has been greatly extended and 

 increased by recent experiments of a more elaborate character. 

 These were carried out in the respiration chambers previously 

 referred to, the object being to determine the actual amounts 

 of carbon and hydrogen oxidised in the animal's body, and the 

 amount of energy (heat) produced. 



Various forms of apparatus have been used for the purpose. 

 That of Pettenkofer, shown in the illustration l (Fig. 9), consists 

 essentially of a cubic iron box, about eight feet each way. 

 The plates of which it was constructed were riveted together 

 like those of a boiler, and made perfectly air-tight. 



When the subject of the experiment was introduced into 

 the apparatus, a steady current of air was drawn through by 

 means of pumping machinery. The composition of the air 

 entering and leaving the chamber was determined by analysis, 

 and the quantity was accurately measured by large meters 

 designed for the purpose. In this way accurate information 

 was obtained regarding the amounts of oxygen consumed, of 

 carbon dioxide, water, etc., produced, and, inferentially, of the 

 amounts of carbon, hydrogen, etc., stored in the body during 



1 Bulletin No. 21, Office of Experiment Stations, U.S. Department of 

 Agriculture, 



