4 2o SCIENCE PROGRESS 



human thyroid. The presence of iodine may not after all be 

 a matter of supreme significance for the function of the thyroid. 

 It is at any rate so problematic that the whole matter requires 

 careful investigation. No chemically pure substance has been 

 isolated from the gland (28). 



(d) Influence of the thyroid upon metabolism. — Metabolic pro- 

 cesses are distinctly increased by the administration of thyroid 

 substance. There is at first no influence on proteid meta- 

 bolism, but an increase of nitrogenous excretion from increased 

 elimination of nitrogen-holding extractives already present in 

 the body. The body fat is first used up. After a certain period, 

 however, the proteid is also attacked (29). 



(e) Theories as to the function of the thyroids and parathy- 

 roids. — The most generally accepted view is that the thyroid 

 gland furnishes in the form of an internal secretion some 

 substance or substances which are in the human being and 

 some other animals, essential for the maintenance of health. 

 The results of extirpation in human beings and in some animals, 

 the effects of thyroid disease in the human subject (cretinism 

 and myxcedema), combined with the beneficial effects of the 

 administration of thyroid extracts, are strong arguments in 

 favour of this view. 



Nothing positive is known as to the functions of the para- 

 thyroids considered separately from the thyroids. 



(iii) The Pituitary Body 



(a) Structure and development. — The pituitary body consists of 

 three portions : (1) The anterior lobe proper ; (2) an intermediate 

 portion ; (3) the nervous portion. 



The epithelial portion of the pituitary body is differentiated 

 into two distinct parts : an anterior lobe proper, consisting of 

 solid columns of cells, between which run wide blood-channels; 

 and an intermediate portion, which lies between the anterior 

 lobe and the nervous tissue of the pituitary, forming a closely 

 fitting investment of the latter. 



The anterior lobe contains cells which are either clear or 

 granular. The intermediate portion consists of finely granular 

 cells arranged in layers of varying thickness closely applied to 

 the body and neck of the posterior lobe and to the under surface 

 of adjacent parts of the brain. Colloid material occurs between 

 the cells of the pars intermedia. 



