264 WATER ITS RELATION TO METABOLISM 



Thus the increased output takes place during the working 

 period. 



Atwater calculates that if the whole of the water, derived from 

 the oxidation of hydrogen in the food metabolised, were given out 

 from the lungs and skin it could not equal more than J of the 

 water given out during rest, and J of that given out during work. 



The water given out as sweat can be calculated if the carbon 

 and water loss from the lungs and oxygen uptake is found by 

 analysis, and the loss of body weight determined. The difference 

 between these two losses is the sweat, supposing neither urine nor 

 faeces are passed and no food taken. 



Rubner measured the loss of water from the lungs and found 

 it to be 17 grm. per hr. during rest, 28 grm. on reading aloud, 

 and 34 grm. on singing. 



The relative humidity and the movement of the atmos- 

 phere have a most important relation to the evaporation of the 

 sweat and the regulation of body temperature. 



The means of heat regulation depend on the rate of heat 

 production and heat loss. The former is the chemical and the 

 latter the physical method of regulation. The rate of loss 

 depends, firstly, on conduction and convection, and this depends 

 on the relative temperature and conductivity of the surface 

 of the body, and of the substance with which it is in contact, 

 and in the case of air on the rate of its motion, i.e. winds, 

 draughts. The rate of heat loss is proportional to the sq. rt. 

 of the velocity of the wind (Schuckmann). The velocity of the 

 wind round houses in towns is rarely more than 10 per cent, of 

 that in the open. The wind, by cooling the skin, increases the 

 rate of metabolism and promotes the growth of subcutaneous 

 fat the natural garment of the body. Coddling over fires in 

 hot rooms and avoidance of cold and wind has the opposite 

 effect enfeebles the heat-regulating mechanism, lowers the rate 

 of metabolism, and lessens the power of resisting the invasion of 

 the tubercle bacillus. Secondly, the rate of loss depends on 

 radiation, and this in its turn upon the specific radiating power 

 of the surface of the body, and upon the difference in temperature 

 between the latter and surrounding objects. Thirdly, on evapora- 

 tion, which depends on the amount of sweat evaporated, and 

 upon the relative humidity of the air and the rate of its 

 movement. The evaporation of 1 grm. H 2 at body temperature 



