THE BIOLOGICAL CONTROL OF LIFE 41 



or that human characteristic is transmitted to offspring 

 according to definite predictable rules. 



Another illustration may be taken from a very dif- 

 ferent field. For many years scientific attention has 

 been directed to the puzzling occurrence of dull, dwarfish 

 children called * cretins/ who are sad failures in their 

 main business of growing up. After many years of 

 inquiry it was discovered that the common feature in 

 these defective children from different places and 

 different races was an imperfect development of the 

 thyroid gland or ' throat-sweetbread ' — a small paired 

 organ which lies beside the larynx or Adam's apple and 

 furnishes to the blood passing through it an indispensable 

 internal secretion or hormone. This small organ, which 

 certainly does not look as if it were of much importance, 

 is essential to the health and normal development of both 

 body and mind. This knowledge gained, the practical 

 application speedily followed. It was found that the 

 cretin children, and others tending in the same direction, 

 could be rescued by giving them, as part of their food, 

 the thyroid glands of sheep. As Sir William Osier, one 

 of the masters of modern medicine, put it, " The results 

 as a rule are most astounding — unparalleled by anything 

 in the whole range of curative measures. Within six 

 weeks a poor, feeble-minded, toad-like caricature of 

 humanity may be restored to mental and bodily health. 

 The skin becomes moist, the pulse-rate quickens, and 

 the mental torpor lessens." And this is not an isolated 

 instance of medical magic. 



