DISTRIBUTION OF IODINE IN THYROID GLAND 177 



vago-sympathetic nerve was stimulated just above the point at which 

 it was cut near the eighteenth tracheal ring. It was easily possible to 

 vary the strength of the electrical stimulus so that a current of such a 

 strength was employed as just to bring about the ocular changes char- 

 acteristically associated with stimulation of the cervical sympathetic 

 nerve. Mendenhall (15) has emphasized the markedly toxic effects of 

 ether on the sympathetic nervous system. In a preparation like that 

 last described the sensitivity of the cervical sympathetic nerve to the 

 depressant action of ether could easily be demonstrated. A tetanizing 

 current of rather low frequency from a Stoelting inductorium was made 

 for 5.5 seconds at intervals of 11.8 seconds throughout the period of 

 stimulation. At the end of most of these experiments a vein of the 

 stimulated lobe, in most cases without the ligation of its companion 

 veins, was cannulated and the effect on blood flow of stimulation of the 

 gland under the same conditions as those employed in the experiment 

 was observed. In ten out of sixteen experiments no difficulty was en- 

 countered in demonstrating a vasoconstriction in the gland on stim- 

 ulating the vago-sympathetic nerve with an electric current of the same 

 strength and delivered at the same rate as that used in the previous 

 stimulation period. The threshold of excitability for the vasoconstrictor 

 nerves of the thyroid gland appears to be considerably lower than that 

 for the submaxillary gland as reported by Gruber (16). The relatively 

 low threshold of excitability of the vasoconstrictor nerves of the thyroid 

 to epinephrin stimulation has been observed by Gunning (17). 



From table 5 it may be seen that stimulation of the vago-sympathetic 

 nerve with the sympathetic trunk intact above the eighteenth tracheal 

 ring has no appreciable effect on the concentration "of iodine in the stim- 

 ulated lobe. In a number of experiments it was unequivocally demon- 

 strated that vasoconstrictor fibers to the gland were being stimulated; 

 yet such stimulation did not alter detectably the iodine content of the 

 lobe subjected to stimulation. 



Effect of stimulation of the vago-sympathetic nerve on the concentration 

 of water in the thyroid gland. In table 6 may be found data relative to 

 the effect of stimulation of the vago-sympathetic nerve on the concen- 

 tration of water in the thyroid gland. I was unable to find that stimu- 

 lation had any effect on the concentration of water in the stimulated 

 lobe even in experiments in which vasomotor changes were definitely 

 proved to result from stimulation. 



