228 



METHODS OF INVESTIGATION. 



barrel, an uninterrupted stream of fresh air enters the chamber A, and the air 

 in the chamber, mixed with the respired gases, escapes toward the barrel. Con- 

 nected with the afferent opening z is a set of Liebig's bulbs d, filled with a solution 

 of potassium hydrate through which the entering air passes and is deprived 

 of its carbon dioxid, so that the subject breathes air completely free of carbon 

 dioxid. Upon leaving the efferent opening b the air is first conducted through 

 the tube e, in which the aqueous vapor is absorbed by sulphuric acid, and its 

 amount may be determined by the increase in the weight of the tube. Then the air 

 passes through the potassium-bulbs f, where all the carbon dioxid is absorbed. 

 The tube g, filled with sulphuric acid, is intended for the purpose of absorbing 

 the aqueous vapor conveyed by the air from f . The increase in weight of f -f- g 

 represents the weight of the absorbed carbon dioxid. The volume of air inter- 

 changed may be estimated from the contents of the barrel. 



(6) Regnault and Reiset's apparatus (Fig. 87) consists of a bell- jar R, in 

 which is placed the animal (dog) to be experimented upon. Surrounding this 



CaCh 



FIG. 87. Diagrammatic Representation of Regnault and Reiset's Respiration Apparatus. 



jar is a cylinder g g, which may be used for calorimetric observations, a 

 thermometer t being introduced for this purpose. The bell-jar has leading into 

 it the tube c, through which is introduced a measured quantity of oxygen (Fig. 

 87, O), which (Fig. 87, CO 3 ) has given off to the potassium hydrate any remaining 

 admixture of carbon dioxid. The oxygen in the measuring vessel O is forced 

 toward the bell-jar R by a solution of calcium chlorid, coming from a basin pro- 

 vided with large bottles (Ca C1 2 ). From R pass the tubes d and e, connected by 

 rubber tubes with the communicating potash-bottles (K OH, k o h), which 

 may be alternately raised and lowered by means of the scale-beam w. By these 

 means the air is aspirated from R, and the carbon dioxid is absorbed by the solution 

 of potassium hydrate. At the end of the experiment the increase in weight of 

 the bottles represents the quantity of carbon dioxid expired. The amount of 

 oxygen inspired is measured directly in the measuring vessel O. Finally, the 

 manometer f shows whether there is a difference between the air-pressure within 

 the jar and that on the outside. 



(c) The most complete apparatus is that of v. Pettenkofer (Fig. 88) . A cham- 

 ber Z, made of metal and provided with a door and a window, has an opening for 

 the entrance of air at a. A double suction-pump P P 1( driven by steam, renews 



