EVOLUTION OF CARBON DIOXIDE. 53 



after injury there is a marked increase in the respiration which, with slight 

 oscillations, rises to its maximum in 26 hours. After that period there is a 

 slow decline in the amount of carbon dioxide evolved until by the beginning of 

 the fourth day it is normal again (fig. 5). 



Two other partial series were made in connection with the variation in 

 acidity which is consequent upon wounding. It has been shown that acidity 

 is influenced by traumatic reaction and that the acidity is considerably lower 

 at the time of greatest respiration. The results of these two series (table 37) 

 are consistent both with the previously described respiration effect and with 

 the acidity determinations (table 21). Averaging the results in this case the 

 maximum is at 24 hours after injury, at which time the acidity is lowest. 

 As the healing processes set in and the carbon dioxide decreases in amount 

 there is evidence of a rise in acidity. Entirely aside from the question of 

 wound respiration in general, in this case the increase in carbon dioxide is 

 very likely due to the more rapid oxidation of the organic acids, which, by 

 reason of the exposure of a larger surface of tissue to the air, are more readily 

 broken down. In that respect, as in the case of carbon-dioxide evolution in 

 sunlight, the phenomenon may not be wholly a respiratory one in the strict 

 sense of the term. That we have to do here with an oxidation process is 

 brought out clearly by the experiment given in table 38, which shows the 

 wound respiration in relation to absence of oxygen. At both 20 C. and 35 C. 

 the evolution of carbon dioxide is greatly reduced in an atmosphere of pure 

 nitrogen ; in the first case to less than one-third that in air and in the second 

 to less than half. The respiration in the absence of oxygen is about that 

 which would be expected in uninjured tissue. 



DIURNAL PERIODICITY IN RELATION TO TEMPERATURE. 



Three continuous series were carried through over periods of more than 24 

 hours under temperature conditions representing the diurnal change of an 

 average day at Tucson in late spring (tables 39, 40, and 41). The objects were 

 to plot the daily march of respiration and to determine how slow but con- 

 tinuous changes in temperature would affect the rate of carbon-dioxide pro- 

 duction. The series was, of course, made with the receiver darkened, as it 

 was not desired to complicate the question with photosynthetic action. In 

 order that the temperature changes as they affect the tissues themselves could 

 be noted, the thermometer in each case was thrust into one of the joints in the 

 receiver. This was effected by boring a small hole longitudinally through a 

 joint, w r hich was then laid aside for a few days until the wound had healed. 

 The temperature within the cactus joint lagged behind the air temperature in 

 the receiver by about half an hour. In the tables it is the temperature within 

 the tissue that is given. 



The most interesting point which developed was the lag in the reaction to 

 the temperature changes. In each case the minimum rate of carbon-dioxide 

 production was about an hour later than the minimum temperature within 

 the joint. Similarly the maximum respiratory activity was delayed. The 

 accompanying graphs (fig. 6) bring this out clearly. In comparing these 

 results with the diurnal acidity curve, it appears that the time of lowest 

 acidity, especially when the acidity has been falling rapidly, must also 

 be the time of the greatest evolution of carbon dioxide. But it must not 



