THYMUS AND THYROID GLANDS. 353 



its effect on goitre, contains no iodine. Second, the proportion 

 of iodine in the colloid matter may be artificially increased to 

 even ten tunes the normal amount without occasioning any 

 increase in the activity of the preparation ; * while artificially 

 iodized proteids show relatively little action. In this connec- 

 tion the recent work of Roos f deserves attention. He found 

 that the effects of equal quantities of dried thyroid in increas- 

 ing the nitrogenous metabolism of dogs were apparently pro- 

 portionate to the content of iodine in the glandular tissue fed. 

 Equally varying was the efficacy of the different preparations 

 in reducing the size of parenchymatous goitres. These facts, 

 however, by no means compel the conclusion that the char- 

 acteristic action is due to the iodine present; with equal 

 probability we may assume corresponding variations in the 

 accompanying active groups to which the iodine is perhaps 

 attached merely as a factor of secondary importance. Under 

 this interpretation of the facts known, it is not necessary to 

 follow Roos J in attributing the favorable action of thymus to 

 the minute traces of iodine occasionally found in preparations 

 of that gland. 



STJMMAHY. 



1. The accessory thyroids in man may contain both rela- 

 tively and absolutely more iodine than the thyroid proper of 

 the same individual. 



2. The observations that the thyroids of newly-born 

 children contain no iodine are confirmed. 



3. There is no satisfactory evidence to show that the care- 

 fully isolated thymus of man or animals contains iodine. 

 Traces found by other observers were presumably due to 

 adherent thyroidal tissue. 



* Hutchison, Journal of Physiology, 1898, xxiii, p. 178. 

 t Roos, Zeitschrif t f iir physiol. Chemie, 1899, xxviii, p. 40 ; cf. also Oswald, 

 Ibid., 1899, xxvii, p. 40. 



t Roos, Zeitschrift fur physiol. Chemie, 1899, xxviii, pp. 60-61. 



