REGULATORS 599 



tendency to flushing from increased vaso- motor activity, 

 sweating, increased secretion of urine, often prominence of the 

 eyeballs and enlargement of the thyreoid forming a soft goitre. 

 The rate of metabolism is markedly accelerated, proteins are 

 more rapidly broken down, and carbohydrates are too rapidly 

 mobilised and hence sugar may appear in the urine. The 

 symptoms may all be explained in terms of the action of 

 thyreoid extracts. The prominence of the eyeballs in man is 

 probably due to stimulation of visceral muscular fibres in the 

 eyelids by which they are unduly opened and the bulging of 

 the eyeball allowed to take place. It may occur in lower 

 animals. 



In simple goitre the thyreoid tissue undergoes a slow hyper- 

 trophy and no general symptoms are manifest. 



(6) Nervous Control. — Taking as indices (a) the sensitising 

 action of the internal secretion of the thyreoid on the abdominal 

 sympathetic nerve ; and (6) the decrease in the amount of iodine 

 in a lobe, it has been found that stimulation of the nerves 

 supplying the gland leads to an increased output of the 

 internal secretion. 



The thyreoid thus seems to produce an internal secretion 

 rich in iodine which exercises a stimulating effect upon the 

 metabolism. 



Whether it does so by a direct action, or whether through 

 the autonomic nervous system, upon which it undoubtedly 

 acts, cannot at present be decided. 



4. Pituitary. 

 The true pituitary is the anterior part of the pituitary of 

 anatomists. 



1. Development.— It is formed by a hollow outgrowth from 

 the roof of the buccal cavity, and it lies in front of and embraces 

 the hypophysis. 



2. Structure. — It consists of (1) an anterior jmrt, composed of 

 dense columns of cells of two kinds— (a) the chief cells, which 

 are large and do not stain readily; (6) the chromophil cells 

 which contain granules, some staining with acid, some with 

 basic stains. It is very vascular. (2) A 2^^'>^s intermedia, 

 separated from the former by a cleft and applied closely to 



