2 A RESPIRATION CALORIMETER. 



Experiments in which the balance of income and outgo of nitrogen 

 alone is determined are comparatively simple. The intake of nitrogen is 

 that in the food and drink ; and since it is commonly accepted by physiol- 

 ogists that none of the nitrogen from food or body material is eliminated 

 in gaseous form, the only sources of output which are ordinarily con- 

 sidered are the urine and feces. Doubtless because of the ease with 

 which such experiments may be conducted, the number of nitrogen 

 metabolism experiments that have been made is very large. 



For a study of the metabolism of fats and carbohydrates, however, an 

 estimate of the gaseous output of the respiratory products, i. c. , carbon 

 dioxide and water, and of the intake of oxygen, is, as has been stated, 

 also necessary, in addition to the analyses of food, drink, and excreta. 

 These determinations can not be even approximated without the use of 

 apparatus specially constructed for the purpose, known as respiration 

 apparatus, which is usually of necessity somewhat complicated. 



For the determinations of income and outgo of energy, which is 

 measured in terms of heat, special forms of apparatus, designated cal- 

 orimeters, are necessary, and these are likewise complicated. 



Since the more complete metabolism experiments are not so easily 

 carried on, they are much less numerous than the simpler nitrogen 

 metabolism experiments ; still the number in which more or less com- 

 plete balances of income and outgo of matter, or energy, or even both, 

 have been determined is relatively large, and several different forms of 

 respiration apparatus and calorimeters have been used. It is not pos- 

 sible to give here a detailed historical review of the development of 

 such apparatus, and indeed it is hardly necessary, as extensive bibli- 

 ographies and descriptions have been published elsewhere. It will be 

 sufficient for the present purpose to mention these and to point out the 

 different types of apparatus. 



Accounts of various types of respiration apparatus have been com- 

 piled by Zuntz ' and Jaquet.* The various forms of apparatus which 

 are of sufficient size to permit study of the respiratory changes in man 

 or large animals may be divided into four classes. 



In the first class the subject is confined in a closed chamber for 

 varying periods of time. The carbon-dioxide content of the air is de- 

 termined at the beginning and again at the end, and the volume of the 

 inclosed space being known, the amount of carbon dioxide eliminated 

 during this period is thereby readily calculated. The apparatus of 

 Chauveau* and Laulani^ 4 were constructed on this plan. 



1 Hermann's Handbuch der Physiologic, 4, part 2, pp. 88-162. 

 1 Ergeb. der Physiol. (1903), 2, part i, pp. 458-469. 

 ' Traite" de Physique Biologique, 1, p. 744. 

 4 ijle'ments de Physiologic, p. 355. 



