84 Inside the Living Cell 



present in the living organism also act as oestrogens. Some are sur- 

 prisingly simple — for example, the compound stilboestrol, which was 

 discovered by Lawson and Dodds to be more active than the natural 

 hormone. What common characteristics these molecules have has 

 not been discovered. 



The last source of hormones I shall mention is the pituitary gland — 

 a complex gland situated in a bony hollow at the base of the skull. 

 The posterior portion of the gland controls the amount of water 

 retained by the body by regulating its flow through the kidneys. The 

 effects of the anterior portion are so extensive that it has been called 

 by Sir Walter Langdon Brown *the conductor of the whole endocrine 

 orchestra'. It stimulates, and indeed is necessary for, the action of 

 most of the other glands, since it is found that if the anterior part of 

 the gland is removed, the thyroid, the suprarenal cortex, the islets 

 of Langerhans, and the ovaries or testes all atrophy. It controls 

 growth, in that an excess of pituitary action causes gigantism, while a 

 deficiency is dwarfing. A number of distinct hormones have been 

 isolated having distinct actions in stimulating the various hormone- 

 producing glands. 



There is a hormone which stimulates the sex glands; others which 

 stimulate milk production, and still others which control various 

 phases of the sexual cycle and control growth. One of them (adreno 

 cortico tropin — acth) stimulates the adrenal cortex to liberate the 

 hormones which protect the body from the effects of stress, and 

 relieve the symptoms of rheumatism. This pituitary substance is 

 much too rare and costly for general use in relieving rheumatism — 

 400,000 pigs being required to yield one pound of the hormone! 

 Unlike most of the others, the pituitary hormones are proteins, but 

 Dr C. H. Li has found that in some of them the protein molecule is 

 made up of smaller parts which possess the activity. 



The chemical control of the body thus presents a very complicated 

 picture and much remains to be learnt about it. The ductless glands 

 produce a wide variety of substances and their actions are far from 

 simple. A single hormone may be concerned in a great variety of 

 different processes, and the glands also interact with each other. The 

 pituitary, as we have seen, acts as a stimulator of the others; the 

 proper working of the body always depends on a delicate balance 

 of the working of the various glands. 



Since they are often quite simple compounds, and are also, 

 generally speaking, indifferent to species, the hormones seem to be 

 relics of a primitive system of control. The thyroxin of the frog is 

 the same as that of cows and human beinss. The sex hormones of 

 the fowl are much the same as those of the horse. Very litde is known 



