i88 SECTIONAL ADDRESSES 



0-686 when it was eating. Gorer in a complete review of the subject 

 concludes that there is adequate proof of some such conversion. 



No doubt exists as to the conversion of carbohydrate into fat in the 

 animal body, and respiratory quotients above unity have been freely 

 allowed. But even here difficulties have arisen, because it is difficult to 

 imagine that such a conversion begins de novo and just at the point when 

 the value of the respiratory quotient exceeds unity and that the metabolism 

 of fat ceases completely at exactly the same point. Cathcart and Marko- 

 witz have pointed out this difficulty, but their observations on the rise of 

 the respiratory exchange and respiratory quotient after giving sugar, 

 which iiad been previously studied by Higgins, do not prove that such 

 conversion takes place below a respiratory quotient of unity. They 

 qualify their criticism of the theory in the following words : ' We do not 

 wish to cast doubt on the validity of the calculations of indirect calorimetry 

 when the experiments extend over several hours ; indeed, we are whole- 

 hearted believers in the method under these conditions. We even believe 

 that when conditions in the body are stabilised (as they presumably are 

 in the post-absorptive condition when basal metabolic rates are commonly 

 determined) agreement between indirect and direct calorimetry will be 

 close. But where metabolism is actively proceeding in the organism, as 

 may occur in short experiments following food, this close agreement 

 cannot be expected.' Krogh and Lindhard go further than Cathcart and 

 Markowitz when they suggest that the conversion of carbohydrate to 

 fat on the one hand and fat to carbohydrate on the other begins towards 

 the middle range of respiratory quotients (i.e. 0-90 upwards and o-8o 

 downwards), but it is difficult to see how any argument can be based on 

 observations in which the heat itself was not determined. 



Dale and his co-workers, and Cori and Cori, suggest that the adminis- 

 tration of insulin to depancreatised and normal animals brings, about oxi- 

 dation of carbohydrate and so raises the value of the respiratory quotient, 

 but in depancreatised animals the respiratory quotient may be fairly high 

 — up to about o • 80, so that the power to utilise carbohydrate is not lost. 

 In the more severe forms of muscular work respiratory quotients greater 

 than unity have been observed, which can only mean some reduction of 

 the carbohydrate — a conversion of carbohydrate to fat ; but this is unlikely 

 if carbohydrate is the main source of energy in muscular work, a hypo- 

 thesis that has been put forward to explain quotients up to unity which 

 are obtained when muscular work of moderate intensity is performed 

 (Furusawa). 



A Fundamental Error in Indirect Calorimetry. 



The most complete study of direct and indirect calorimetry in normal 

 man under basal conditions is that made by Benedict and Carpenter. In 

 the experimental work carried out by these observers, the greatest pre- 

 cautions were taken to eliminate, or to compensate for, all known sources 

 of error. The accuracy of the respiratory calorimeters used was checked 



