METABOLISM 219 



minimum activity is taken as a standard. This is called the 

 Basal Metabolism, and is taken as the amount of heat produced 

 by a person lying quietly in bed, protected from extremes of 

 temperature, and having taken no food for 12-15 hours. There 

 has been much discussion as to whether this should be referred 

 to units of body weight or body surface. Apparently it is 

 absolutely proportional to neither of these standards, but per- 

 haps to the "mass of active protoplasm" in the subject. This 

 it is of course impossible to determine experimentally. It has 

 been found however, that the heat production is very nearly 

 proportional to body surface', which easily can be calculated 

 from a formula devised by Du Bois. Under basal metabolism 

 conditions, the normal adult produces very close to 40 calories 

 per square meter surface per hour. A deviation of 10-15% 

 from this standard is still considered normal. Certain diseases 

 are accompanied by marked deviation from this value. In 

 exophthalmic goiter the heat production may run 50-75% above 

 this normal, and in no other disease is it so high. In myxedema, 

 and cretinism, where the thyroid activity is subnormal, the 

 basal metabolism fails to a very low level. This fact is of great 

 value in diagnosis, and in following the effect of treatment. 



Basal metabolism may be determined not only by direct meas- 

 urement of heat eliminated, which involves a costly and elab- 

 orate calorimeter, but also by the method of "Indirect Calor- 

 imetry. " By the measurement of the oxygen consumed and C0 2 

 exhaled by a patient in a given time it is possible to calculate 

 the respiratory quotient. This, when considered with the 

 amount of nitrogen in the urine, coming of course from protein 

 destruction, gives all data necessary to calculate just how much 

 fat, carbohydrate and protein have been burned in the body. 

 Since we know the number of calories produced in the oxida- 

 tion of 1 gram of each of these substances, it is possible to cal- 

 culate the total heat production and thus the basal metabolism. 



Apparatus for Indirect Calorimetry is within the reach, finan- 

 cially speaking, of every clinic, and its use as an aid to diagnosis 

 has become very widespread. 



