GAS INTERCHANGE. 85 



The mature joints showed an evolution of carbon dioxide of 0.11 c.c. per 

 gram-hour fresh weight in the absence of oxygen and of 0.16 c.c. in normal air, 

 while with the young joints the amounts stand, respectively, 0.25 c.c. and 

 0.35 c.c. In comparing these figures with those of the Pettenkofer determina- 

 tions, it will be seen that they are in accord with the latter. With the Pet- 

 tenkofer experiments it will be remembered that at 21 C. about half as much 

 carbon dioxide was evolved in the absence of oxygen as was the case in normal 

 air, while at 30 C. the amounts were nearly equal. In those now under con- 

 sideration the difference in the behavior of the plants in an atmosphere of 

 hydrogen and in normal air is greater than that found at 30 C. and less than 

 that at 21 C. ; but it will be noticed that the temperature is also intermediate, 

 being 27.5 C. The actual quantity of .carbon dioxide evolved is less in these 

 experiments, which were carried on at Tucson in 1912, than in the Pettenkofer 

 experiments which were made in New York. This difference has already been 

 discussed in connection with other determinations and nothing further need 

 be said. Reducing the volume of the gas to weight in milligrams, we have the 

 following figures: mature material in hydrogen, 0.16 mg. per gram-hour fresh 

 weight, in air 0.23 mg.; young material in hydrogen, 0.36 mg. per gram-hour, 

 in air 0.50 mg. These quantities are closely similar to those found in two of 

 the Pettenkofer series (tables 32 and 33), but considerably less than the 

 amounts shown in table 34. 



For the sake of convenience, this evolution of carbon dioxide may be re- 

 ferred to as intramolecular respiration without making a definite statement as 

 to whether or not it is entirely comparable with intramolecular respiration as 

 ordinarily understood. As the hydrogen used in the containers was of a purity 

 of 99.5 per cent, only a very minimal quantity of the evolved gas can be ascribed 

 to the absorption of external oxygen. If the impurity was air, which may be 

 fairly assumed, then the actual percentage of oxygen present was no more than 

 0.1 per cent, an amount which, as has been said, must speedily be absorbed. 

 It has been shown that the acidity as determined by the method employed did 

 not diminish at the rate at which it does in the presence of oxygen, and that, 

 indeed, is what is to be expected. Consequently, the carbon dioxide which is 

 formed does not seem to have come from the breaking up of the acid to the 

 same extent as in the normal cases. It is possible that the preliminary steps 

 in the degeneration of the malic acid may take place, thereby releasing an 

 amount of carbon dioxide, but at the same tune maintaining an acidity that 

 would be evident by the titration method. Whether this is the case could only 

 be determined by a more precise examination of the acid content of the tissue 

 than was attempted. The whole question of the so-called intramolecular 

 respiration in these forms is well worthy of closer study. 



INCREASED OXYGEN SUPPLY AND GAS INTERCHANGE. 



An increased supply of oxygen tends to raise rather than to lower the gas 

 ratio, as is shown by the experiments set forth in table 66. From the results 

 of the experiments on carbon dioxide evolution with the Pettenkofer apparatus 

 it has been seen that the rate of the production of this gas is greatly increased, 

 and this is borne out by the experiments now under discussion. The intake of 

 oxygen is also increased, but it does not keep pace with the larger output of 

 carbon dioxide. Consequently, the gas ratio must rise. 



