PROBLEM 6. Hormones Help Regulate Cell Activities 



247 



Fig. 238 Robert Wadlo-u: at tl.ie age of i) shakhig hands luitl.i a full gruixii man. 

 Before he died he was 8 feet 7 inches tall and weighed 4^0 pounds. Study of these 

 pages will provide an explanation, (acme) 



The effects of thyroxin on the or- 

 ganism have been studied. From experi- 

 ments on goats, pigs, rabbits, and other 

 mammals we know that if the thyroid 

 gJand is removed from a young animal 

 its physical development is interfered 

 with and the reproductive organs do not 

 develop. Its basal metabolism is very 

 much reduced, that is, oxidation is slowed 

 up. Feeding an extract of the thyroid 

 gland to the animal soon after the opera- 

 tion prevents these changes. It is be- 

 lieved that thyroxin acts as a catalyst, 

 speeding up oxidation in all parts of the 

 body. 



In the lower vertebrates removing the 

 thyroid has equally striking effects. Tad- 

 poles without a thyroid gland never de- 

 velop into frogs. They remain as tadpoles 

 and fail to develop reproductive organs. 

 On the other hand, feeding thyroid ex- 

 tract to normal tadpoles has the opposite 



Front of voice box 



Right lob 

 of 

 thyroid g 



(trach 



dpipe 

 eo) 



Fi(i. 239 Thyroid gland. How would you de- 

 scribe its position? What in/portafit hormone 

 does it produce? 



