1054 ABSORPTION 



The Effect of Sleep. — Sleep does not affect the metabolism of the 

 proteins to any extent, as is shown by the fact that the total nitrogen 

 excreted remains about the same. Instead, there appears a slight 

 reduction in the output of endogenous purine nitrogen, indicating a 

 lessened destruction of nuclear substances. Contrariwise, the ingo 

 of oxygen and outgo of carbon dioxid are markedly diminished, an 

 indication that the tonicity and activity of the muscles and glands are 

 considerably reduced. 



The Effect of Temperature. — Within narrow limits the met?.bolism 

 of the warm-blooded animals is increased by a cold and decreased by 

 a warm outside temperature, but this result is only obtained if the 

 body-temperature is not greatly altered thereby. Extreme varia- 

 tions in the outside temperature, which in turn produce a material 

 change in the body-temperature, affect the metabolism in a reverse 

 manner. This need not surprise us, because the body constantly 

 attempts to retain its normal temperature of about 37.0° C. A cooling 

 of the air gives rise to a greater loss of heat and hence, a more intense 

 metabolism must immediately be instituted to counteract this effect. 

 Contrariwise, an increased temperature of the atmosphere lessens the 

 loss of heat and, consequently, less heat need be produced. But, in 

 case this heat-regulatory mechanism is overcome, an excessive fall 

 in the body-temperature invariably diminishes the oxidations and heat 

 production, whereas an unusual rise increases these processes. The 

 body having been sufficiently cooled, all chemical processes within it 

 come to a standstill. Evidently, in the presence of a well-balanced 

 heat-regulatory mechanism, any deficiency in the body-temperature 

 is made up at the expense of the non-nitrogenous constituents of the 

 tissues. This is shown by the fact that the consumption of oxygen 

 and elimination of carbon dioxid are increased, while the nitrogenous 

 excretions in the urine remain practically the same. 



The Effect of Age and Sex. — The output of energy is low in the 

 new-born, but increases rapidly during the first year until it reaches 

 its maximal value at about the sixth year. Subsequent to this time, 

 it decreases rather rapidly until the twentieth year and then more 

 slowly until late in life. This steady decline is interrupted only at 

 the time of puberty, when the metabolism is temporarily intensified. 

 The output of energy by the female is about 4.3 per cent, below that 

 of the male. 



The Effect of Muscular Exercise. — The metabolism is materially 

 increased even by ordinary degrees of work, although the protein 

 waste is no greater than during rest. After excessive exercise, on the 

 other hand, the latter is considerably increased, embracing urea, am- 

 monia, creatinine, and even uric acid and purine bases. This contra- 

 dicts the view of Liebig, implying that the greater energy hberated 

 during muscular work finds its source in a break-down of the muscular 

 tissue, and must, therefore, be performed at the expense of an increased 

 metabolism of the proteins. Such a result, however, is never obtained 



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