330 Mr. G. H. Knibbs : Mathematical Analysis of 



capacity for saturation of air at say 37° C. is 46*65 mm. r 

 which implies generally a considerable margin for taking up 

 moisture from the body. 



The loss of carbon doubtless depends upon the rate of 

 metabolism, and hence may be expected to show considerable 

 changes from its mean value towards the limiting conditions,, 

 viz., for very high and very low temperatures. 



The resolution of the matter must therefore, in its essence,, 

 be mainly empirical. The function expressing rate of evapo- 

 ration ought probably to deal with evaporation losses from the 

 skin and from the lungs separately, as well as losses of carbon 

 from the lungs. The data must be temperature, capacity of 

 the air for further saturation, the condition of air movement,, 

 and characteristics of the body (viz., weight, form, and other 

 special characters). With these a quantitative solution is 

 possible, but the type of formula necessary must be deduced 

 from the results and their rational interpretation, and not 

 wholly a priori. 



Although within certain limits the body may be regarded 

 as a thermostat, its surface is by no means thermostatic, and 

 its variations of temperature depend not only upon the 

 temperature of the surrounding air but also upon the air 

 movements on the surface of the body. Apart from the 

 consequences arising from the difference in temperature of 

 the liquid at the surface of the body, no doubt the reactions 

 on the arterioles and capillaries profoundly affect the 

 conveyance of liquid to the surface. In fact, we have an 

 evaporating surface with considerable variations of tem- 

 perature and degrees of porosity, reacting quickly to external 

 and internal conditions. 



Thus in any complete solution on first principles we should 

 have to take into account the mean temperature of the surface, 

 and its variations with air temperature and air movement. 



It will on the whole be probably more convenient to regard 

 these conditions as among the physiological elements of 

 variation, since in any conceptual case (taken to represent 

 the phenomena) the body must be supposed in the same state 

 for identical external conditions, any physiological factor 

 being treated independently. The temperature of the evapo- 

 rating surface is probably in all cases sensibly less than 

 37° C. by an amount which itself depends on the temperature,, 

 saturation capacity, and movement of the air. Hence in an 

 empirical solution we may include these elements in the 

 factors representing external conditions. They will influence 

 the form of the functions representing the effect of these 

 elements. 



