425 



whereby the logarithmic notation of S0rensen can be converted at sight 

 into true concentrations. It would be advisable to redraw the figure on 

 semi-logarithmic paper and so enable the reading to be taken to two 

 places of decimals. For example, to convert pHQ-1 into C H , pH = 6 is 

 C H = 10~ 6 ; 0-7 cuts the diagonal line opposite 0-2; therefore 



pKot 6-7 = C H of 0-2xlO-. 



Estimation of the Surface Area of the Body. Rubner announced that 

 the amount of heat produced by an animal is proportional to its superficial 

 area. This law of surface area has rendered necessary the accurate deter- 

 mination of the skin surface in most metabolism experiments. 



Since the surface of a figure varies as the square, and that of volume as 

 the cube of its linear dimensions, it follows that 



where S = surf ace, F = volume and K = constant, or, as weight (W) varies 

 directly as volume, 



S = K 2/W*. 



Meeh, from sixteen experiments, suggested that K should be = 12-3 for 

 adults ; and Lissauer used the value 10-3 for children. The average error 

 of this calculation is about 16 per cent. 



ZO 30 40 $0 60 70 99 88 WO 110 



FiG. 85. Du Bois Graphs for Estimating the Area of Body-Surface. 



The brothers Du Bois covered the body-surface of their subjects with 

 " tights " and applied melted paraffin. Paper strips were affixed to 

 prevent change of area during the process of removing the " shell." The 

 model of the surface, cut into pieces sufficiently small to be flat, was photo- 

 graphed upon squared paper of uniform thickness. The weight of each 

 square on the paper was known. The darkened portions of the paper 

 were carefully cut and weighed, and from this was calculated the area of 

 body surface. The formula resulting from this work involved nineteen 

 measurements. From this they have evolved a two -measurement formula 

 on which the appended chart is based (Fig. 85). 



The Field of Vision (see p. 225). The extent of the field of vision may be 

 measured approximately as follows : 



Describe a semi-circle on a blackboard with the free ends of the line 

 finishing at one side. Mark the centre of the circle at the edge of the board, 



