154 THE STUDY OF ANIMAL LIFE CHAP. 



the thyroid gland does not develop are cretins, dwarfed 

 and unintelligent, but if they eat prepared thyroid of calf 

 and the like or extract thereof they begin to develop 

 both physically and mentally. They go on progressing 

 so long as the artificial supply is kept up. Ingrafting a 

 small portion of a normal thyroid has sometimes worked 

 well. Disease of the thyroid results in the large neck- 

 swellings known as goitre and in a serious disorder 

 called myxcedema, both which are treated medically by 

 thyroid diet and injections. An important colloid sub- 

 stance produced in the thyroid is called iodo-globulin, 

 interesting chemically because of the presence of iodine. 

 There are also minute quantities of arsenic in combina- 

 tion with nuclein-substances. 



Some of the prescriptions of ancient physicians have 

 often provoked a smile : that the coward should devour 

 the raw heart of the lion (if obtained by the patient 

 himself cure was certain), that the weakly should eat 

 the heart of an ox (as they often do), that the lethargic 

 should dine on ram's brains, that the jaundiced should 

 try the liver of a fox, and so on. Yet surely there is 

 some approach to this in the modem thyroid treatment. 



Another good illustration of organs of internal secretion 

 is afforded by the two adrenal bodies which occur in 

 the vicinity of the kidneys, on their upper edge in man. 

 They are markedly divided into a cortical or peripheral 

 and a medullary or central portion with different func- 

 tions. When they are diseased in man there is deteriora- 

 tion of the skeletal muscles, a discoloration of the skin, 

 and nervous disturbance. The central part produces a 

 substance called adrenalin. If this is injected in very 

 minute quantities into the circulation, it affects the 

 sympathetic nervous system, and thereby quickens the 

 heart-beat. There is a rise of blood-pressure which is 

 due to a constriction of the muscular fibres of the minute 

 blood-vessels or arterioles, and this has led to the use of 

 adrenalin in surgery or in stopping a commonplace 

 bleeding of the nose. The discovery of the role of inter- 

 nal secretions, for which Starling proposed the term 

 " hormones," has had a very important influence on 



