THE THYEOID GLAND AND ITS DISEASES 487 



apparatus has a value at least five times as great, because in the latter case 

 it is equivalent to the loss or gain of so much pure oxygen. 



The calculation of the basal metabolic rate is very simple. Know- 

 ing the volume of air expired by the patient in a minute (the ventila- 

 tion rate) and the percentage of carbon dioxid and oxygen in the expired 

 air, it is possible to calculate the volume of oxygen absorbed by the 

 patient in one hour, as well as the corresponding amount of carbon dioxid 

 produced. Since the respiratory quotient, that is the ratio between the 

 volume of carbon dioxid produced and the volume of oxygen absorbed, 

 indicates the kind of food being burned at the time of the determination, 

 and since by means of calorie tables the calorific value of one liter of 

 oxygen absorbed by the body in the burning of these substances is known, 

 the total heat production each hour can be readily calculated. The total 

 number of calories must be divided by the surface area, a factor corre- 

 lated with the patient's height and weight. The number of calories for 

 each square meter of body surface each hour must then be compared with 

 the normal standards of comparison which are dependent on the age and 

 sex of the patient. For convenience, basal metabolic rates are expressed 

 in percentages of the normal, and when the heat production is greater 

 than the normal the percentage is plus, and when less than normal the 

 percentage is minus. (Sandiford). 



Some difficulty has been experienced in making satisfactory determi- 

 nations of the area of body surface and hence of the heat production. 

 Eubner (a) suggested that the heat production of an individual is pro- 

 portional to his surface area. For the determination of the surface area 

 Meeh proposed the formula: Surface area in square centimeters = 12.3 

 (a constant) X weight in grams 2 ' 3 . There were, however, some errors 

 in calculations based upon this formula, due in greater part to the fact 

 that the height of the subject was neglected. As a result of further 

 studies Du Bois and Du Bois (a) (b) devised a formula based on height 

 and weight by means of which the surface area can be calculated with an 

 average error of 1.7 per cent. This formula is: 



0.425 0.725 



A = W X H X 71.84 



where A is the surface area in square centimeters, W is the weight in 

 kilograms, H is the height in centimeters and 71.84 is a constant. On 

 the basis of this formula they then constructed a height-weight chart 

 by means of which the surface area can be estimated at a glance. Du 

 Bois, using this new height-weight chart for the determination of the 

 surface area in conjunction with his standards of normal basal metabolism 

 with regard to age and sex, further showed that the metabolism of 

 normal persons can be predicted with an accuracy of 10 per cent. 

 This fact has been confirmed both by Means (a) and by Boothby. 



