180 HARRY BENJAMIN VAN DYKE 



in the percentage of iodine in the lobes of dried thyroid gland of the dog 

 is 0.015 per cent in this vicinity. If we consider as non-significant all 

 differences in the percentage of iodine in dried thyroid of 0.010 per cent 

 or less we see that stimulation, while causing an apparent diminution 

 in the concentration of iodine in 16 or 36.4 per cent of the glands, and 

 an apparent increase in the concentration of iodine in 10 or 22.7 per 

 cent of the glands, had no effect on the iodine concentration of 18 or 

 40.9 per cent of the stimulated glands. The greater part of the experi- 

 mental data presented may be briefly summarized in table 7. 



The differences which I found above appear to be due to normal 

 variations in the concentration of iodine in the two lobes of the dog's 

 thyroid gland. The average percentage difference in the concentration 

 of iodine in the two lobes of the dog's thyroid gland depends on a num- 

 ber of factors such as the type of gland, the time of year and the feed- 

 ing of iodine. Hence I am forced to conclude that if stimulation of the 

 vago-sympathetic nerve in the dog has any effect on the concentration 

 of iodine in the thyroid gland, that effect is considerably less than the 

 normal variation in the iodine content of the stimulated and control 

 lobes. The presence of normal variations relatively so much greater 

 than the variations which may follow stimulation renders valueless the 

 application of more refined methods of iodine determination in the study 

 of the effect of stimulation of the cervical sympathetic nerve on the 

 concentration of iodine in the thyroid gland. 



SUMMARY 



1. Periodic stimulation of the isolated vago-sympathetic nerve by 

 an induced current of a moderate to strong intensity over a period of 

 from three to three and a half hours does not appreciably alter the 

 distribution ratio of iodine between cells and colloid. 



2. The findings of Rahe, Rogers, Fawcett and Beebe (2) and of Watts 

 (3) that stimulation of the cervical sympathetic nerve for a comparable 

 period of time reduces the concentration of iodine in the stimulated 

 lobe were not confirmed. Watts' assertion that such stimulation reduces 

 the water content of the stimulated lobe was not confirmed. 



3. Conclusions as to the direct secretory control which the cervical 

 sympathetic nerves exercise on the thyroid gland are based in no small 

 measure on the alleged effect of stimulation of the cervical sympathetic 

 nerve on the iodine content of the gland. Conclusions having such a 

 basis apparently are untenable. 



