1 62 GROWTH 



asexual types, are explained by the absence of the reproductive 

 hormones. 



An example of an extraordinary growth stimulation followed 

 by abrupt inhibition and atrophy of particular reproductive tis- 

 sues may be mentioned at this point. During childbearing there 

 is an excessive growth of the muscle of the walls of the uterus. 

 The total mass increases several hundred per cent above the 

 normal size of the resting organ. Immediately following birth 

 this tissue stops growing and rapidly retrogresses. Within a few 

 days it is resorbed and returns to approximately the normal 

 size. The whole cycle of growth and rapid decline is primarily 

 dependent upon the presence or absence of particular but un- 

 identified hormones. The facts are not so clearly determined, 

 but possibly it is a part of the same process that the chorionic 

 villi and placental membranes of the embryo grow into the lin- 

 ing membranes of the uterus forming a very elaborate nutri- 

 tional apparatus of blood vessels and blood channels, with a 

 very considerable amount of new tissue. At birth this growth 

 usually ceases, the excessive chorionic mass also retrogresses, 

 and the placental tissues are shed. The process is almost miracu- 

 lous in its efficiency. Occasionally, however, bits of these chori- 

 onic tissues, which by the rule ought to degenerate and disap- 

 pear, in fact continue to grow without check. They become can- 

 cerous in fact. Fragments may be displaced and grow parasitic 

 in new positions. In the end they destroy the life of the unfortu- 

 nate victim. Obviously some chemical factor in the inhibitory 

 control of the embryonic membranes has failed with disastrous 

 and fatal results. 



VI. The Pituitary Gland 



Always among large groups of human beings one finds an 

 occasional man or woman of unusual height and size. The ordi- 

 nary height of normal adults is between 5 feet 4 inches and 6 

 feet. In every selected group of young men, as, for example, in 

 the student cadet battalions of the University, we are impressed 



