614 RESPIRATORY RATE OF SCIATIC NERVE OF FROG 



An elaborate apparatus, to which the inventors have given the name 

 "biometer, " was used to collect the carbon dioxide produced by the 

 tissue and to bring it into contact with a drop of barium hydroxide 

 solution. The formation of the precipitate of barium carbonate was 

 observed under the microscope. The time required for the formation 

 of an amount of carbon dioxide sufficient to cover the drop with a 

 film of barium carbonate was used as a measure of the rate of car- 

 bon dioxide production. With this method, Tashiro has estimated 

 the frog's sciatic nerve to give off carbon dioxide at the rate of 5.5 

 X 10~^ gm. per 10 mg. of tissue per 10 minutes. He compares this 

 result with the data obtained by other workers for the rate of 

 carbon dioxide output of the entire animal and of muscle tissue. 

 From such a comparison he concludes that nerves have not only a 

 carbon dioxide metabolism equal to that of other tissues but greater.^ 

 With a view to getting at the facts regarding carbon dioxide pro- 

 duction in nervous tissue, the writer has employed the indicator 

 method developed by Haas^ in Osterhout's laboratory and subse- 

 quently used by Osterhout and his pupils.^ In practice a quantity 

 of the indicator, phenolsulfonephthalein, sufficient to give the 

 desired tint was added to Ringer's solution. A liter of this solution 

 in a glass-stoppered bottle was brought to the required reaction 

 by a few drops of 0.1 N NaOH. For the measurements, small 

 tubes of Pyrex glass calibrated to hold 3 cc. of solution were used. 

 These were closed with paraffined corks. Both corks and tubes 

 were boiled repeatedly in neutral water, and before being used were 

 washed in alcohol, then in ether, and finally the corks were saturated 

 with hot neutral paraffin. The tubes were next tested for several 

 hours by filling with the tinted solution, corking, and inverting. 

 Those in which any color change occurred were discarded. This pro- 

 cedure was carried out before each experiment. In the experiments, 

 the rate of carbon dioxide production was determined by measuring 

 the time necessary for the tint to change from pH 7.8 to 7.4. The 



® Mathews, A. P., Physiological chemistry. A text-book and manual for stu- 

 dents, New York, 1915, 590. 



" Haas, A. R., Science, 1916, xliv, 105. 



7 Osterhout, W. J. V., Gustafson, F. G., Brooks, M. M., Thomas, H. S., Irwin, 

 M,, /. Gen. Physiol, 1918, i, 171-209. 



