SOCIAL AND WORLD ASPECTS 211 



Section of the British Association, Sir Arthur Keith 

 (1920) discusses the basis of differentiation of man- 

 kind into racial types, and shows how the character- 

 istic racial differences are probably connected with 

 differences in the secretions of the endocrine glands. 

 He points out that the characteristic differences of 

 feature, build, and colour cannot (for the most part) 

 have been evolved directh^ by natural selection of 

 variations, and elaborates the view that the differences 

 observed are a result of variations which have arisen 

 in the organs of internal secretion. These glands are 

 now known to control in a marvellous manner the 

 processes of development and functioning of the body. 

 The principal of these organs are as follow^s : (i) The 

 thyroid (a gland in the neck, astride the trachea); 

 (2) the parathyroids (four small glands close to the 

 thyroids); (3) the pituitary (a small reddish organ at 

 the base of the skull), of which the anterior and 

 posterior lobes have different functions ; (4) the pineal 

 body;* (5) the suprarenal capsules, over the kidney's, 

 consisting of cortex and medulla, with different origins 

 and diverse functions ; (6) the islets of Langerhans 

 in the pancreas ; (7) the interstitial tissue of the gonads . 

 These glands pour directly into the blood which 

 bathes them extremely minute quantities of their 

 various secretions, and the latter control in remark- 

 able fashion both the development and functioning, 

 not only of the body, but also to some extent of the 

 brain and mind. 



The first instance in which the form of the body 

 was found to be influenced by an internal secretion 

 was that in which a pathological condition of the 

 pituitar}^ was shown to be the cause of the condition, 

 known as acromegaly, in which there is enlargement 

 of the bones and flesh of the hands, feet, and face. 



* A small gland, about the size of a pea, under the brain, 

 resting on the anterior corpora quadrigemina. 



