362 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



simplest explanation in the supposition that the muscles are less active during 

 sl< ep. The muscles do less work in the way of contractions, and, in addition, 

 probably suffer a diminution in tonicity which also affects their total metab- 

 olism. 



Effect of Valuations in Temperature. — In warm-blooded animals variations 

 of outside temperature within ordinary limits do not affect the body-tem- 

 perature. A full account of the means by which this regulation is effected 

 will be found in the section upon Animal Heat. So long as the temper- 

 ature of the body remains constant, it has been found that a fall of outside 

 temperature may increase the oxidation of non-proteid material in the body, 

 the increase being in a general May proportional to the fall in temperature. 

 That the increased oxidation affects the non-proteid constituents is shown by 

 the fact that the urea remains unchanged in quantity, other conditions being the 

 same, while the oxygen-consumption and the C0 2 -elimination are increased. 

 This effect of temperature upon the body-metabolism is due mainly to a reflex 

 stimulation of the motor nerves to the muscles. The temperature-nerves of 

 the skin are affected by the fall in outside temperature, and bring about 

 reflexly an increased or a diminished innervation of the muscles of the body. 

 Indeed, it is stated 1 that unless the lowering of the temperature is sufficient 

 to cause shivering or muscular tension no increase in the C0 2 -excretion results. 

 This fact suffices to explain, therefore, the physiological value of shivering 

 and muscular restlessness when the outside temperature is low. The fact that 

 variations in outside temperature affect only the consumption of non-proteid 

 material falls in, therefore, with the conception of the nature of the metab- 

 olism of muscle in activity, given above. When the means of regulating 

 the body-temperature break down from too long an exposure to excessively 

 low or excessively high temperatures, the total bodv-mPtabolism, proteid 

 as well as non-proteid, increases with a rise in body-temperature and de- 

 creases with a fall in temperature. In fevers arising from pathological 

 causes it has been shown that there is also an increased production of urea as 

 well as of C0 2 . 



Effect of Starvation. — A starving animal must live upon the material pres- 

 ent in its body. This material consists of the fat stored up, the circulating 

 and tissue proteid, and the glycogen. The latter, which is present in compara- 

 tively small quantities, is quickly used, disappearing more or less rapidly 

 according to the extent of muscular movements made, although in any case it 

 practically vanishes in a few days. Thereafter the animal lives on its own 

 proteid and fat, and if the starvation is continued to a fatal termination the 

 body becomes correspondingly emaciated. Examination of the several tissues 

 in animals starved to death has brought out some interesting facts. Voit took 

 two cats of nearly equal weight, fed them equally for ten days, and then killed 

 one to serve as a standard of comparison and starved the other for thirteen 

 days: the latter animal lost 1017 grams in weight, and the loss was divided as 

 follows among the different organs : 



1 Johannson: Skandinavisehr* Archiv fiir Physioloyie, 1897, Kd. vii. S. 123. 



