BY DR. BURDON-SANDERSON. 339 



on hydro-carbons, and have the additional advantage that, 

 although they are of variable temperature, their heat produc- 

 tion is as active as that of warm-blooded animals, are specially 

 adapted for the investigation of the relation between heat pro- 

 duction and oxidation. 



Under many circumstances which preclude the use of this 

 method alone, it is of value in combination with that of direct 

 measurement, to be immediately described ; for the informa- 

 tion it affords, even when the nutritive substances consumed 

 are partly nitrogenous, is trustworthy. If the ingestion of 

 nutritive material is regular and uniform, it affords a rough, 

 but otherwise reliable, indication of whatever variations may 

 occur in the activity of the chemical vital processes. 



It will be readily understood, that these indications occur 

 later than the causes which produce them ; so that it is not 

 until some time after any increase or diminution of oxidation, 

 that the corresponding increase or diminution of the discharge 

 of carbonic acid manifests itself. The mode of gauging the 

 discharge of carbonic acid in the animal body has been de- 

 scribed in the previous chapter. In the application of the re- 

 sults of such determinations, it must not be forgotten that the 

 absolute values obtained are meaningless. Their use is limited 

 to the interpretation of direct calorimetrical measurements. 



116. Direct Estimation of the Quantity of Heat 

 produced by an Animal in a given Time. The second 

 method (to which alone the term Calorirnetry is strictly appli- 

 cable), consists in the direct estimation of the quantity of 

 heat (heat units) given off by an animal in a given time. The 

 subject of observation is placed lor a measured period in a 

 chamber, which is so constructed that while it is continuously 

 supplied with air for respiration, it is surrounded on all sides 

 by a mass of water, the weight and temperature of which are 

 known. The construction of such a chamber (Calorimeter) 

 can be readily understood from the diagram, fig. 265. 



A, is a box of zinc plate, in which the animal is placed, the 

 size varying according to the animal it is intended to receive. 

 If for rabbit or small dog, it is 15 J inches long by 12 inches 

 wide, and 13 inches high. It possesses two openings, one of 

 which is in the lid and communicates with a large gasometer, 

 into which air is constantly injected by a Bunsen's water air- 

 pump. The other is in one end, and opens into an exit tube 

 (D), which after surrounding the box twice, terminates in a 

 flexible connector, by which the air which has passed through 

 the chamber escapes. The section of this tube, the purpose of 

 which is to secure the condensation of the aqueous vapor dis- 

 charged from the lungs and skin, is oblong and rectangular; 

 in order that it may present to the water by which it is sur- 

 rounded as large a surface as possible. The inner box (A) is 



