Carboliyc Irate ML-taliolisiii in relation to the Thyroid Claud 65 



crease in the total CO, excretion as the distribution over the various 

 periods that is significant. All these observations point clearly to the 

 conclusion that during the " early " stage of experimental liyperthyroidism 

 more of the ingested carbohydrates are oxidised than in the normal 

 animal. 



The same condition of the gaseous metabolism durinir the earlv staore 

 of experimental hyperthyroidism is seen in the experiments with Hat 2 : 

 the prolonged po.st-prandial rise of the CO, excretion is especially notice- 

 able on the third day of th^'roid feeding. In the case of Hat 4 the observa- 

 tions on the normal animal gave the least uniform results, and the first two 

 days of thyroid feeding show no obvious chantre from the normal, either 

 as regards the curve of the respiratory (|Uotient or that of the COj excre- 

 tion. The latter is slightl}' increased, but the quotient curve is actually a 

 little below the normal. There is only the characteristic tilt-up of the curve 

 in the eitjhth hour after a meal, which is noticeable in all the three cases of 

 " early "stages of experimental hyperthyroidism which we have investigated. 



In the " later " stage of experimental hyperthyroidism the gaseous 

 metabolism undergoes a complete change, and the interpretation of the 

 results becomes more difficult. The most obvious change is a general 

 marked increase in both the COg excretion and the Og absorption, and 

 this is the effect w^hich has so frequently been described as the result of 

 thyroid administration. The explanation usually given — if it is an ex- 

 planation — is that the thyroid hormone increases the processes of oxida- 

 tion. The further analysis of this increased gaseous exchange by hourly 

 observations shows that there is not only a quantitative but also a (juali- 

 tative change. The curve of the CO2 excretion retains its characteristic 

 features, in fact the post-prandial rise is even more marked. But the Og 

 absorption, instead of remaining more or less constant, now also shows a 

 pronounced post-prandial rise and subsequent fall. The two curves which 

 in the normal animal are convergent 1 run parallel. The respiratory 

 quotient curve thus becomes flattened out, although it still shows a 

 maximum. But this maximum does not now occur in the third hour after 

 feeding at the beginning of the experiment as in the normal animal, but 

 is delayed. In Rat 4 with three days' feeding it is found in the fourth 

 hour, in Rat 1 with five days' feeding in the sixth hour, and in Rat 3 with 

 five days' feeding in the seventh hour, so that in this last case the curve 

 for the respiratory quotient becomes inverted. A notable point is tliat the 

 respiratory quotient curve may be at a high level as in Rat 1 (first .series) 

 and Rat 4, or at a low level as in Rat 1 (.second series) and Rat .S. 



The high-level curves, where the re.spiratory quotient remains above 

 0-9 from the third to the seventh hour, clearly indicate an increased oxida- 

 tion of carbohydrates. But that explanation does not account in itself for 

 the great increase in the total gaseous exchange. And at first sight it does 

 not seem possible to reconcile this explanation with the low-level curves. 

 » This applies to the curves of the weights of CO^ and Oj. 

 VOL. XL, XO. \. — 1917. ^ 



