164 INHIBITORY NERVES AND CO2 PRODUCTION 



physiological saline solution consisting of 100 cc. of m/2 NaCl plus 

 2 cc. of m/2 CaCU and containing phenolsulfonephthalein to indicate 

 the hydrogen ion concentration. 



We note the time required to produce the color change which indi- 

 cates a change in the hydrogen ion concentration from the initial 

 value pH 7.8 to 7.4. This gives a normal standard of the rate of 

 development of CO2 which can be compared with the rate at which 

 the ganglion produces the same change while the inhibitory nerves 

 are being stimulated. 



Owing to the many failures to secure preparations of the ganglion 

 with the inhibitory nerve uninjured and functioning, the following 

 technique was adopted. Upon opening the dorsal carapace and peri- 

 cardium the inhibitory nerves were identified by faradic stimulation; 

 they were then secured distally with a fine silk hgature. The peri- 

 cardium was removed from the whole heart and the cardiac ganglion, 

 from its posterior end to the middle of the second segment, was dis- 

 sected from the heart. This left functional connection of the ganghon 

 with the first muscular segment which therefore continued to beat. 

 The ganglion, free from all extraneous tissue, was now looped over 

 tiny hooks on a slender glass rod which was cemented into the stopper 

 of the indicator tube and the inhibitory nerves connected with it 

 were laid across fine platinum wire electrodes passing through and 

 cemented into the stopper. The nerves were again stimulated to 

 determine whether they still inhibited the ganghon and stopped the 

 beats of the first muscular segment. If the dissection has been suc- 

 cessful it is only necessary to snip the nerve cord anterior to the point 

 at which the inhibitory nerves enter to obtain the desired preparation 

 of the ganglion mounted and ready for introduction into the tubes 

 containing the solution with the indicator (phenolsulfonephthalein). 

 We now determine the rate of the desired color change.^ 



' In a simpler preparation the ganglion alone was used and stimulation applied 

 to its anterior end. This usually produces inhibition but stronger faradization 

 may stimulate, so that the analysis of the results of the respiratory changes was 

 sometimes problematical, therefore we have confined our published results to 

 those obtained by the method described in the text. 



