398 THE WONDER OF LIFE 



regulated. In the beautiful growth of a crystal in the 

 midst of its solution, there is some degree of regulation 

 in relation to the already existing architecture. Although 

 we may not understand much about it, we see that the 

 growth of the crystal is not higgledy-piggledy addition, 

 but an orderly and proportioned crystalhzation. But this 

 is far more deeply true of organic growth, which imphes a 

 regulated series of phenomena, occurring in a certain 

 sequence and within certain hmits. If the sequence be 

 disturbed or the hmits be crossed, then there is something 

 abnormal. The regulation is comparable to that which 

 we see in the erection of a properly-designed building — 

 there is a style and a plan to be adhered to, there are laws 

 of proportion to be respected, there is even a normal rate 

 which must not be disregarded. In the same way, the 

 regulation of organic growth has reference to the specific 

 constitution of the organism (its structural organization 

 on the one hand and its characteristic metabolism on the 

 other), and that means that it has reference to the past 

 history or evolution of the organism. This subtle quahty 

 of regulatedness is one of the criteria of organic growth, 

 and it seems to many biologists to remove it far from the 

 mere multiplication of chemical substances, or from the 

 continued action of a ferment as long as material to ferment 

 is supphed. 



One of the ways in which the regulation of growth is 

 brought about within the organism is by means of inter- 

 nal secretions or ' hormones '. These are produced by 

 glands or glandular tissues in various parts of the body, 

 and are passed into the blood. They are transported hither 

 and thither and, when they come into close quarters with 

 susceptible parts, they stimulate or hinder growth. Thus 



