Apparatus For Estimating Carbon Dioxide 143 



on the other plate in such a way that one part of the nerve lies across 

 the electrodes of the glass plates as shown in Fig. i, page 120. In 

 this way, when the plates are hung on the electrodes i> and m, any 

 desired nerve can be stimulated with the induction current. These- 

 plates are now hung on the electrodes in each chamber, and the usual 

 procedure is followed for the cleaning and the washing of the appara- 

 tus to make it CO 2 free. After the connection between the two 

 chambers is closed by means of stop-cock L, the nerve in chamber 

 A is stimulated by the current. Then if one can watch over the 

 surfaces of the drops carefully from the start, he finds the first deposit 

 of the carbonate on cup d of chamber A in which the stimulated nerve 

 is placed. Later, the total amount of the precipitates grows much 

 larger in the case of this cup. This increased output of the carbon 

 dioxide from the stimulated nerve, thus observed, can be duplicated 

 by repeating the similar experiment, after exchanging the chambers, 

 as usual. This comparative estimation can be more accurately made 

 by exact quantitative measurement, the method for which the follow- 

 ing will illustrate. 



(c) For Quantitative Measurement of Gas. The detailed 

 method is exactly analogous to that of apparatus i. Here we use 

 chamber B as the respiratory chamber and A as the analytic cham- 

 ber. Barium hydroxide should be introduced into chamber A only 

 at d, and the stop-cock F is always closed except at the time of wash- 

 ing. The pressure should be adjusted by mercury burette T, or by 

 the potash bulb of the nitrometer. In case the mercury burette is 

 used, the remaining volume in the respiratory chamber should be 

 recorded. 12 The introduction of a known amount of gas from the 

 respiratory chamber B to the analytic chamber A is accomplished 

 by withdrawing the mercury from C into a very narrow graduated 

 cylinder, while the stop-cocks L G and H are opened. After a quick 

 adjustment of the mercury burette to equalize the pressure, the stop- 

 cock L is closed and the presence of carbonate is looked for exactly 

 in the same manner as described in connection with the other appara- 

 tus, determining the minimum volume that gives the precipitate for 

 the known mass of tissue for a known time. 



12 The bulbs are marked at the point where their capacity became 15 c. c. 

 by introducing mercury. The variation of capacity can easily be read by noting 

 the mercury burette. 



