156 GROWTH 



III. The Parathyroids 



In the human there are four tiny glands called the -para- 

 thyroids which lie on the surface, or slightly imbedded in the 

 surface of the thyroid. Each of these is not more than three or 

 four mm. in diameter, yet the presence and normal function 

 of these glands is necessary to the growth and development 



Figure Si. Curve showing the increase in the calcium content of the blood due to 

 injections of parathyroid extract at intervals indicated by the arrows. Clark, Collip, 

 and Scott. Permission of the Journal of Biological Chemistry. 



of the individual. If they are surgically removed in animals or 

 man or undergo degeneration from X-ray or other treatment 

 then a train of nervous symptoms with severe cramps, muscular 

 twitchings, and tetany follows. These attacks may and in gen- 

 eral do end in asphyxiation and death. 



Collip 8 has prepared a purified extract of the parathyroids 

 which when given to experimental animals with or without 

 parathyroids greatly increases the amount of calcium in solution 

 in the blood. When the glands are entirely removed, the cal- 

 cium content drops below normal to 3 or 4 mg. per cent as 

 compared with the normal calcium of 8 to 10 mg. per 100 cc. 



