The Body-Machine and Its Work 357 



chemical messengers of this kind. One of the most interesting 

 illustrations is in connection with the milk in the mother's breasts. 

 How does the mammal mother come to have this rich development 

 of her milk-glands just at the moment when it is needed? It has 

 been discovered that, as soon as she becomes pregnant, the ovaries 

 begin to discharge a hormone into her blood, which finds its way 

 to the breasts and stimulates them. Probably the embryo itself 

 also produces hormones which pass into the mother's blood, and 

 serve a useful purpose up to the time of birth. 



Finally, there is a remarkable and long neglected little body 

 in the head, the "pituitary body," which is a rich laboratory of 

 hormones. It controls the growth of tissues by stimulating them. 

 When it is removed from an animal, the body becomes feeble and 

 undersize. On the other hand, some rather unfortunate people 

 have their pituitary body overgrown, or over-active, and they 

 develop unpleasantly large faces, hands, and feet, or become 

 "giants." 



Such, as far as one can tell it in so brief a space, is the 

 tale of the wonderful mechanisms in the body. Even the skin, 

 which binds and protects this marvellous system of parts, is a 

 remarkable organ when one has time to study it thoroughly. On 

 the tender eyelids of a young child it is as thin as tissue paper, yet 

 on the palms of some "horny-handed son of toil" it will produce 

 protecting cells until it becomes an eighth of an inch thick. It is, 

 moreover, rich in sweat-glands (which, as we saw, are most im- 

 portant for regulating the temperature of the body), lubricating 

 or sebaceous glands, corpuscles for the sense of touch, and little 

 pits in which take root the hairs which were once of great service 

 to the body. Every internal surface also has its lining, or skin: 

 tough where toughness is required, but so fine in the right places 

 that gases and fluids can pass through it for breathing and nutri- 

 tive purposes. "The proper study of mankind is man," said a 

 great poet ; and we may surely add that we know no more interest- 

 ing study in the universe. 



