64 Cramer and M'Call 



being oxidised almost exclusively, and then gradually falls, until it reaches 

 in the eighth hour the level of the fasting animal with a quotient .of 

 about 075, indicating: the almost exclusive combustion of fat. Move- 

 ments of the animal increase both the COg excretion and the O^ absorption, 

 so that any restlessness of the animal during the period of observation 

 will produce slight irregularities in the curves of the COg excretion and 

 Og absorption, whereas the respiratory quotient remains unaffected. 

 These irregularities, resulting in a slight increase in both COg excretion 

 and Og absorption, can be noted in several experiments, especially during 

 the last hour of the period of observation, when, as stated above, the 

 animals were slightly restless from hunger. 



The effect produced by thyroid-feeding shows two distinct phases, 

 which may be called the " early " and the " later " stages respectively of 

 experimental hyperthyroidism. In our experiments the early stages were 

 observed during the hrst two or three days of thyroid-feeding, the later 

 stages, from the third to the .sixth day. It must be understood that this 

 " later " stasfe, which will be discussed here, does not refer to the extreme 

 effect which can be produced by prolonged feeding for several weeks with 

 large doses of thyroid gland, and which leads to enteritis, great emaciation, 

 listlessness, and eventually death. In our experiments thyroid-feeding 

 was never carried to this extreme stage, and during the entire period of 

 observation the animals remained in good condition : they were lively, ate 

 their food with avidity, and the fteces were well formed. With Rat 1 

 observations were made in the "later" stage, with Rat 2 in the "early" 

 stage of thyroid-feeding, while in the case of Rat 4, and especially of Rat 3, 

 the observations extend over both stages. The observations on Rat 3 may 

 therefore be considered first and in some detail. 



During the " early " stage, which in the case of Rat 3 extends over the 

 fir.st two days of thyroid-feeding, the hourly curve of the respiratory 

 quotient resembles that of the normal animal. There is a rapid rise 

 immediately after a meal and a slow fall. There are, however, certain 

 significant differences. The post-prandial rise is maintained for a longer 

 period ; indeed, on the first day of thyroid-feeding the re.spiratory quotient 

 is higher in the fourth hour than it is in the tliird, whereas in the 

 normal animal the quotient obtaining in the third hour is never exceeded 

 at any subsequent period. There is a similar irregularity during the 

 eighth hour, the last respiratory quotient being higher than that of the 

 preceding (seventh) hour. In the case of Rat 3 the curve for the thyroid- 

 fed animal lies at a higher level than that for the normal, but that, as 

 will be seen, is not invariably the case. These changes in the respiratory 

 quotient curve are due entirely to corresponding changes in the COg 

 excretion. The post-prandial rise in the COg excretion is more prolonged 

 in the thyroid-fed animal. The O^ absorption remains fairly constant, and 

 is not markedly affected. The total COg excretion during the entire 

 period of observation is slightly increased, but it is not so much the in- 



