Carboljydmte Metabolism in it'latii>n to tlir Thyroid (llaiid 61 



we must arrive per exclusionem at the conclusion that they are oxidised. 

 Or we must, assume the existence of a hitlu-rtcj unrecognised depot of 

 carbohydrates functioning in a manner entirely ditl'erent from the recog- 

 nised de})ots in tlie liver and the muscles. The following observations 

 were made in order to see whether this conclusion of an increased 

 oxidation of carbohydrates as the result of thyroid-feeding ran b«- 

 demonstrated experimentally. 



It must be clearly realised that such an incieasrd oxifiation ><i carbo- 

 hydrates could not be due, for reasons which have been given above, to a 

 stimulating ettect of the thyroid hormone on the oxidative processes in 

 the cells, but would have to be looked upon as the result of the iidiibition 

 of the glycogenic function of the liver. This, it is true, runs counter to 

 all accepted conceptions of carbohydrate metabolism : it is, in fact, the very 

 reverse of what one would expect to find. The pro])lem is therefore of 

 interest not only in relation to the action of the thyroid secretion, but 

 raises the wider (jue.stion of the correctness of our current conceptions of 

 carbohydrate metabolism. 



EXPEKtMENT.AL PaKT. 



An increased oxidation of carbohydrates uncomplicated by any <jther 

 changes in metabolism is not known to give ri.se to any very obvious 

 manifestations. It is therefore not so easily recogni.sed or demonstrated : 

 not so easily, for instance, as the reverse condition of a diminished 

 oxidation of carbohydrates. Under the simplest conditions one might 

 expect to find that the respiratory quotient should maintain itself after a 

 meal containing carbohydrates for a longer time at the initial high level 

 which indicates an oxidation of carbohydrates and which is due mainl}' to 

 increased excretion of CO2. This was the plan which was followed in 

 this investigation. It may be pointed out at once, however, that that 

 expectation can be fulfilled only if, as stated above, the increased oxidation 

 of carbohydrates is uncomplicated by any other changes in metabolism. 



The observations were made on rats. These animals, being omnivorous. 

 are especially suitable for such observations. The estimation of the 

 gaseous metabolism was made by the method of Haldane and Pembrey, 

 which is well adapted to observations on small animals. Some modifica- 

 tions were found to be an improvement. Instead of using pumice-.stone 

 saturated with concentrated sulphuric acid for the absorption of water, the 

 current of air was passed through concentrated sulphuric acid in a squat 

 wash bottle constructed on the principle of Folin's apparatus for the 

 absorption of ammonia. The carbonic acid was absorbed by a tulje 

 containing first a pad of glass wool soaked in strong caustic soda and then 

 soda lime. The precautions recommended by Haldane and Pembrey 

 (weighing against dummy tubes, controls, etc.) were observed. Since with 

 the short hourly periods of observation adopted in these experiments the 

 excretion of COg and HgO amounted only to a few decigrammes, it was 



