GAS INTERCHANGE. 75 



oxygen. The greatest contrast will naturally be found between those experi- 

 ments where the temperature, acidity, and rate are low and those where all 

 three are high. For example, at 28 to 30 C. with a total acidity of 1.17 

 per gram dry weight, the gas ratio is 0.43 with the evolution of carbon dioxide 

 amounting to 0.452 c.c. per gram dry weight. At 40 to 41 C., with the total 

 acidity of 2.66 and evolution of carbon dioxide of 2.572 per gram dry weight, 

 the gas ratio is 1.20. If the material used in the high-temperature experi- 

 ments had chanced to have been of higher acidity, no doubt the contrast would 

 have been even greater, That these differences exist is not astonishing, for 

 the actual rate of gas interchange which accompanies the disruption processes 

 connected with the breaking down of the acids must naturally be greater when 

 the acidity is high than when it is low. The acids are undoubtedly the source of 

 at least a considerable part of the carbon dioxide which is given off, so it is 

 evident that when there is less actual acid present in the tissue there could 

 not under any circumstances be so much carbon dioxide formed. 



Attention is called to the fact that in discussing the general averages set 

 forth in table 49 the four experiments at 40 to 41 C. have not been included, 

 since only one series of relatively high acidity was carried on at this temper- 

 ature. They are not, moreover, w r holly comparable with the experiments 

 carried on at a similar temperature which have already been discussed in con- 

 nection with temperature effects. The experiments under consideration at 

 present were made from fresh material at Tucson, while those cited earlier 

 were carried out in New York from material collected in Tucson at another 

 season of the year and kept for some time in the laboratory. They are, how- 

 ever, instructive in contrast with the Tucson experiments, in which both the 

 ratio and the temperature were low. 



ACIDITY AND RATE OF GAS INTERCHANGE. 



Arranging the data from the Tucson experiments on still another basis, that 

 of acidity, whether it be the acidity of the expressed juice or the total acidity 

 per gram dry or per gram fresh weight, there is additional and corroborative 

 evidence of some of the facts brought out in the preceding discussion. With 

 the higher acidities there are, in general, a higher rate of gas interchange 

 and corresponding higher gas ratios. This is always excepting the 40 to 

 41 C. series, which is not comparable with the others. At the dry weight, 

 total acidity of 1.00 per gram, the ratio is about 0.50; at acidities from 1.01 to 

 3.00 per gram, the ratio averages 0.65; at from 3.01 to 5.00 per gram acidity, the 

 ratio has risen to about 0.80; and finally, in the last group including acidities 

 from 5.01 to 7.85 per gram (the highest found), the ratio is 0.88. To sum- 

 marize, the rate of evolution of carbon dioxide rises in the ratio of 4 to 9 from 

 the lowest acidity to the highest, but (as before) the number of instances aver- 

 aged was not always large enough to be free from the effect of special cases 

 which depart from the usual conditions. 



The series grouped between the temperatures of 31 and 34 C. is again the 

 most consistent for the reason already mentioned, i. e., that a larger number of 

 experiments are averaged. In the four acidity groups given in table 50, 

 the gas ratios at this temperature rise as follows: 0.55, 0.68, 0.80, 0.85. The 

 rate of carbon dioxide evolution rises as follows, 0.297, 1.001, 0.860, 1.475 c.c. 

 per gram dry weight. The irregularity is due to the presence in the second 



