THE VERTEBRATE BODY 



359 



dog, the calcium level of the blood will begin to drop and within a day 

 or two the animal will show involuntary muscular twitching and even- 

 tually convulsions and death. However, the dog can be saved if given 

 an injection of calcium to restore normal functioning of the nerves and 

 muscles. Such a dog in violent convulsions will be wagging his tail 

 happily within a few minutes after the injection. 



Courtesy Good Samaritan Clinic, Atlanta, Georgia 



Fig. 24.8. Cretinism. The three-year old child on the left is stunted both physically 

 and mentally due to a deficient secretion of his thyroid gland since birth. At seven, 

 after four years of treatment with thyroxin, he has lost most of the symptoms of cretin- 

 ism ; and at nine years of age he has become a child of normal body build and mentality. 



To test the effect of too much of this hormone, parathormone may 

 be injected into a dog with a normal supply already in his body. This 

 causes the blood calcium to rise, but it does so at the expense of the cal- 

 cium found in the bones and teeth, causing a weakening of these vital 

 body parts. 



Some types of human convulsions may be due to hypofunction of 

 these glands and may be treated with either parathormone or calcium, 



