86 



METABOLISM AND NUTRITION 



the CO 2 and water excreted and the oxygen absorbed for a whole day or longer, 

 other methods must be used. 



For these purposes several different forms of respiration apparatus have been 

 constructed, among which we shall very briefly describe the following : 



1. [The Apparatus of Atwater and Benedict. In its general features this 

 apparatus, constructed for experiments on human subjects, embodies the princi- 

 ples of one originally constructed by Regnault and Rieset (1849) for experiments 

 on smaller animals. The subject is placed in a respiration chamber of suitable 

 size (5.03 cubic meters capacity) and is supplied with pure air, as indicated in 

 the diagram below (Fig. 40). The air containing the respiratory products is 

 drawn out of the chamber by the pump and is made to pass in turn over H 2 SO 4 

 and soda lime. The gain in weight of the former gives the amount of water 



RESPIRATION CHAMBER 

 o used 



produced 



o deficient 



H 2 I I CO* 



absorbed by absorbed by 



FIG. 40. Schema of the Atwater-Benedict respiration calorimeter. 



eliminated by the respiration and evaporation ; the gain in weight of the latter, 

 the amount of carbon dioxide eliminated. Pure oxygen is next admitted to make 

 up what has been taken out by the subject. To determine exactly how much 

 oxygen has been thus absorbed it is necessary to know how much was contained 

 in the air at the beginning and how. much at the end of the experiment. Sub- 

 tracting the amount present at the end from the total amount supplied i. e., the 

 amount present at the beginning plus the amount admitted gives directly the 

 amount absorbed. 



The respiration chamber in this apparatus is provided also with means of 

 measuring the heat lost from the subject's body by radiation and conduction, so 

 that the entire apparatus is described as a respiration calorimeter. ED.] 



2. The Apparatus of PettenJc offer. This consists of a respiration chamber 

 with a capacity of 12.7 cubic meters into which and from which air is pumped 

 in a continuous stream. The air is analyzed both as it goes in and as it comes 

 out of the chamber, a uniform fractional part of the total volume flowing out 



