METHOD OF ZUNTZ AND GEPPERT 517 



the apparatus. Tests are made before and after in order to 

 determine exactly the amounts of carbonic acid and water 

 given off from the body by the lungs and skin. Proper pro- 

 visions are made for the introduction of food and drink and 

 the removal of the solid and fluid excreta. These are 

 analyzed, not only for nitrogen, fat, carbohydrate and inor- 

 ganic constituents, but also (by means of a calorimeter 

 bomb) for their combustion temperature, thus providing all 

 conditions for a complete report of the energy exchange and 

 metabolism. The reliability of the apparatus is determined 

 for control purposes at the beginning and at the end of each 

 experiment by burning in it an exactly known quantity of 

 alcohol. As evidence of the precision attained with the 

 apparatus it may be added that in the alcohol experiments 

 the average results for three years show the recovery of 100 

 per cent, of the theoretically calculated quantities of carbon 

 dioxide, 103.1 per cent, of the water, and 100.2 per cent, of 

 the heat. 3 Such results are magnificent and marvelous, and, 

 uninteresting as they may sound, may well make the heart of 

 every friend of exact nature-study beat higher. 



Method of Zuntz and Geppert. The great strides in the 

 study of metabolism would have been impossible, however, if 

 the results obtained by these bulky, costly and complicated 

 apparatuses just described were not supplemented by the 

 device of Zuntz and Geppert. The individual experimented 

 upon in this case inhales atmospheric air through a mouth- 

 piece, and the volume of expired air is measured by a gas 

 meter ; the separation of the inspired and exhaled air being 

 accomplished by a suitable valve. A small portion of the 

 exhaled air is automatically taken up from time to time and 

 analyzed volumetrically in two burettes. Besides the per- 

 manent form of the apparatus Zunz also devised a portable 

 form, adapted to studies in travel, mountain trips and at the 



3 Atwater, 1. c., p. 514. 



