THE BIOCHEMISTEY OF THE THYEOID GLAND 251 



tions. These observers declare they can best be accounted for by metabolic 

 changes due to temperature, and further state that "during the colder 

 months of the year the increased physical activity of animals, together with 

 the necessity for maintenance of the normal body temperature in a colder 

 surrounding medium requires an increased metabolism which in turn 

 would no doubt call for an increased output of the., active thyroid mate- 

 rial. Conversely, in the summer months, the demands upon the thyroid 

 being less than the normal rate of production of active principle, would 

 lead to a storing up of the iodin compound." 



Undoubtedly the factor most definitely and quickly able to cause varia- 

 tions in iodin content of the thyroid gland is diet. Baumann (1896) sus- 

 pected high iodin percentages to be due to iodin administration and stated 

 that an increase is caused by feeding with sea-fish, beef-thymus, and espe- 

 cially with thyroid itself or iodothyrin, and with plants the ashes of which 

 contain iodin (sugar-beet), while feeding raw meat to dogs lowers the iodin 

 content. Baumann and Goldman fed a dog raw meat. One thyroid lobe 

 removed weighed 1.92 grams and contained 0.06 mg. iodin. The animal 

 was then fed for a month on dried stock-fish. The remaining thyroid lobe 

 was then removed, weighed 2.5 grams, and contained 2.9 mg. iodin. Roos 

 (1899) and numerous other workers have obtained similar results. Roos 

 pointed out that the glands of carnivora usually contain smaller amounts of 

 iodin than those of herbivora, corresponding to the fact that raw meat 

 contains no detectable iodin. The most striking examples of the results 

 of feeding iodin are those of Simpson and Hunter. Continued daily ad- 

 ministration for six weeks of small quantities of sodium iodid raised the 

 iodin content of a sheep's thyroid from 0.53 to 1.15 per cent (dried tissue). 

 Hunter and Simpson also furnish the best example of such increase on a 

 natural iodin diet. The dried glands of 10 Orkney sheep, which had been 

 allowed to run wild and feed largely on sea-weed, contained amounts of 

 iodin varying from 0.42 to 1.05 per cent of iodin. The average of this 

 particular group was 0.71, a much higher figure than any previously re- 

 corded. The only comparable figures to these maxima are Cameron's for 

 the dogfish Scyllium, 1.16, and the sea-scoter, 1.14. The marine diet of 

 these animals is definitely rich in iodin. The figure for crows (0.75 per 

 cent) was obtained for birds feeding largely on clams, the dried flesh of 

 which contains about 0.01 per cent of iodin. (The harmony between the 

 highest maximal figures suggests that these represent a state of complete 

 saturation of the gland with iodin. ) 



Bourcet (1901), discussing the probable sources of thyroid-iodin, 

 pointed out that traces of the element are contained in various fruits and 

 vegetables, such as fish, mollusks, milk and eggs, and also French wines. 

 Further information as to probable sources of the element is given in the 

 papers of Bohn and of Forbes and Beegle. 



The work of Marine and coworkers indicates that iodin, fed or in- 



