272 THE HUMAN BODY 



ment to be wholly successful for cretins it must be begun quite 

 early in life. 



The Para Thyroids. These are small bodies, usually four in 

 number, which are found near or on the thyroids, sometimes em- 

 bedded within them. The effect of their complete removal is very 

 striking, consisting in the onset of acute toxic symptoms, with 

 muscular convulsions, ending in death. Recently the interesting 

 discovery has been made that the characteristic symptoms fol- 

 lowing extirpation of the para thyroids do not develop if calcium 

 salts are introduced into the blood. It has long been recognized 

 that the element calcium plays a very important, though ill- 

 understood, role in the Body. On the basis of the above observa- 

 tion the suggestion has been made that the para thyroids may 

 function in some way to control the use of calcium by the Body, 

 It is impossible at present to judge finally as to the value of this 

 suggestion. 



The Thymus is a large and conspicuous organ in the new-born 

 mammal. As obtained from calves it constitutes the "neck- 

 sweetbread." Its structure places it unmistakably among the 

 ductless glands. Up to the present its function remains unknown 

 although some evidence has been presented to indicate that it 

 may be associated with the development of the lymphatic system 

 (Chap. XXII). It can be removed without fatal or even tem- 

 porary effect. It was formerly thought to atrophy completely 

 soon after birth, but careful study has shown that some true thy- 

 mus tissue persists in man for years and perhaps throughout life. 



The Pituitary Body (Fig. 62) consists of two lobes, a posterior 

 one, which is an offshoot of the brain, and an anterior one which 

 develops from the pharynx. It seems quite likely that the two 

 lobes are really independent organs physiologically, producing 

 hormones having different effects. A substance has been ob- 

 tained from the posterior lobe which acts specifically upon the 

 kidneys, increasing their output of urine. Effects upon the heart 

 and blood-vessels following injection of extracts of this lobe are 

 also reported. 



Complete removal of the pituitary body in the case of cats and 

 dogs causes a lowering of temperature, muscular twitchings and 

 spasms, difficulty in breathing, general lassitude, and death within 

 a fortnight. The organ has therefore been supposed to form a 



