6 THE THYROID AND 



characteristic if large doses are given. The blood- 

 pressure falls, the pulse becomes rapid (120-140 or 

 more), there may be fever, headache is usual, and 

 there is great mental depression or excitement in 

 many cases. Exophthalmos has been recorded 

 several times after an overdose in man (Beclere, 

 Notthaft), and monkeys (Edmunds). The metaboJic 

 exchanges of the body are increased, consequently 

 there is loss of weight and an increased output of 

 urea, chlorides, and phosphates, and the gaseous 

 exchanges in the lungs are above normal (Roos, 

 Magnus Levy). It will be noticed that the parallel- 

 ism with Graves' disease is very striking. 



CHEMISTRY OF THYROID COLLOID. 



Chemical investigation of the colloid has yielded 

 some important results. The active principle, 

 iodothyrin, has the characters of a globulin (Oswald) 

 which contains a variable proportion of iodine. This 

 element is usually abundant in the thyroid, but 

 almost absent in the other tissues of the body. Its 

 presence was first proved by Baumann of Freiburg, 

 in 1896, and has been abundantly confirmed since. 

 The amount present varies with the species and also 

 with the individual ; in some cases it falls below 

 the limits of chemical recognition. Herbivores 

 possess it in abundance, most vegetables containing 

 iodine. In carnivores it is very scanty. In man it 

 is nearly always present in recognizable quantities, 

 except in young children. Wells finds that the 

 amount varies with the locality, and in general is 

 inversely in proportion to the local prevalence of 



