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TEXT-BOOK OF PHYSIOLOGY 



A Metabolism Experiment. An experiment designed to determine the 

 character and the extent of the chemic transformations which tissue and food 

 materials undergo in their transit through the body is termed a metabolism 

 experiment. It consists primarily in placing an animal under conditions that 

 permit of the collection of all the excretions for purposes of analysis, the 

 object of which is to deduce from the amounts of urea and other nitrogen- 

 holding compounds, and of carbon dioxid excreted, or better, the total nitro- 

 gen and carbon they contain (i) the amount of tissue materials metabolized, 

 during a fasting period of longer or shorter duration and hence from the 

 nitrogen and carbon to calculate approximately, at least, the amounts of the 

 food principles and their ratio one to another that must be returned to the 

 body if nutritive equilibrium is to be restored; or (2) to deduce from the 

 total nitrogen and carbon excreted, the amounts of protein, fat, and carbo- 

 hydrates metabolized, that were contained in the customary foods during an 



FIG. 58. A RESPIRATION CALORIMETER. 



experimental period. If the outcome from the body balances the income 

 the weight of the animal remains stationary from which it is assumed that 

 the amounts consumed constitute a normal diet. Experiments having these 

 objects in view are made possible by enclosing the animal or man in a suit- 

 able^ chamber (Fig. 58) in which there is some provision for collecting the 

 urine and feces, and to which, in addition, there is attached an apparatus 

 for the absorption of water and carbon dioxid, both of which are caused to 

 pass from the chamber through the absorption apparatus under the action 

 of an aspirating pump. Simultaneously fresh air is introduced into the 

 chamber after passing through another absorption apparatus by which it 

 is freed from water and carbon dioxid. As the apparatus is traversed con- 

 stantly by a column of air of normal composition and the waste products 

 removed as rapidly as discharged, the experiment can be continued from 

 six to twenty hours or more without detriment to the subject of the ex- 

 periment. Previous to the beginning of the experiment the animal and 

 the absorption apparatus are carefully weighed. At the end of the experi- 

 ment the urine and feces are collected, weighed and analyzed for their chief 



