248 



How a Co?nplex Aii'mml Uses Food unit iv 



Fig. 240 The picture on the left shows a woman in whojn there was an insufficient 

 secretion of thyroxin later in life. The other picture shows her after treat7nent with 

 thyroxin!. What differences do you note? (Massachusetts general hospital) 



effect. The tadpoles change into adult 

 frogs rapidly without first growing to 

 their full size and the frogs that result 

 are unusually small. This experiment can 

 be performed in the high school labora- 

 tory. It requires the daily careful atten- 

 tion of a student. See Exercise i. 



Too little thyroxin in man. When a 

 child is born with a gland that produces 

 too little thyroxin, that is, when there is 

 a deficiency of thyroxin, the effects noted 

 in experimental animals soon show them- 

 selves. The child is undersized and under- 

 developed physically and it is, also, men- 

 tally deficient. The brain, like the rest 

 of the body, does not develop normally. 

 As in the experimental animal, metabo- 

 lism is decreased and the child becomes 

 sluggish. This condition has been recog- 

 nized for a long time, it is known as 



cret'mimi (cree'ti-nism) and the child is 

 spoken of as a cretin. The feeding of 

 thyroid extract helps to bring about nor- 

 mal growth and development. The ear- 

 lier the treatment is begun the better 

 will be the results. 



In some people the thyroid gland be- 

 gins to secrete less actively in later life, 

 long after the body and the brain have 

 reached their full development. Such 

 people are not mentally defective, al- 

 though they may be slow-moving and 

 slow-thinking because their basal metab- 

 olism is far below normal. Since the rate 

 of oxidation is reduced they tend to be- 

 come overweight. Very small amounts 

 of thyroid extract will remedy this con- 

 dition. The extract is so extremely pow- 

 erful in its effect that only a competent 

 physician should prescribe it. 



