18 STUDIES ON RESPIRATION. IX 



solution does not affect respiration, his data show an increase in res- 

 piration of 41 per cent. 



The writer, in his experiments on Aspergillus niger, used NaCl and 

 CaCl2, as well as mixtures of the two salts. For measuring the pro- 

 duction of CO2 the apparatus described by Osterhout^ was employed, 

 in which the material is placed in one tube and the indicator in an- 

 other.^ This method is very accurate and simple. Care must be 

 exercised to prevent any alkali from passing over from the tube con- 

 taining it into the indicator tube, as this would vitiate the results. 



By adding an indicator to the tube containing the fungus it can be 

 shown that an acid is produced which is non-volatile (or practically 

 so) since it does not disappear when a current of air (free from CO2) 

 is passed through the liquid for 15 or 20 minutes (under these con- 

 ditions CO2 would disappear in 5 minutes or less). 



The apparatus is so constructed that a non-volatile acid cannot 

 affect the color of the indicator which is being matched by the ob- 

 server. The question may arise, however, whether the production 

 of such an acid has any bearing on the interpretation of the results. 

 If it is borne in mind that the problem is to ascertain the changes 

 produced in the output of CO2 under the influence of reagents it is 

 evident that we need not consider the production of other acids 

 except as intermediate stages or as by-products whose study is a 

 problem by itself. This problem always exists, for wherever respi- 

 ration goes on organic acids and other substances are produced. It 

 seems best for the present to confine the investigation to the produc- 

 tion of CO2, leaving the study of other substances to the future. 



The rate of production of CO2 is obtained by taking the reciprocal 

 of the time required to produce a definite change of color in the indi- 

 cator tube.^ 



The fungus was grown and handled as previously described,^ except 

 that water distilled from a hard glass flask was used in place of tap 

 water. The fungus, which forms a mat on the surface of the cul- 



4 Osterhout, W. J. V., /. Gen. Physiol, 1918-19, i, 17, 171. 



^ In this investigation five drops of a 0.01 per cent solution of phenolsulfon- 

 ephthalein were added to 10 cc. of water. This solution was then used for com- 

 parison with the buffer tubes, which contained the same amount of indicator. 



« Gustafson, F. G., /. Gen. Physiol., 1918-19, i, 181. 



