Ill] GROWTH AND CATALYTIC ACTION 135 



further passing word upon the essential fact that certain chemical 

 substances have the power of accelerating or of retarding, or in 

 some way regulating, growth, and of so influencing directly the 

 morphological features of the organism. 



Thus lecithin has been shewn by Hatai*, Danilewskyf and 

 others to have a remarkable power of stimulating growth in 

 various animals; and the so-called "auximones," which Professor 

 Bottomley prepares by the action of bacteria upon peat appear 

 to be, after a somewhat similar fashion, potent accelerators of 

 the growth of plants. But by much the most interesting cases, 

 from our point of view, are those where a particular substance 

 appears to exert a differential effect, stimulating the growth of 

 one part or organ of the body more than another. 



It has been known for a number of years that a diseased 

 condition of the pituitary body accompanies the phenomenon 

 known as "acromegaly," in which the bones are variously enlarged 

 or elongated, and w^hich is more or less exemplified in every 

 skeleton of a '"giant" ; while on the other hand, disease or extirpa- 

 tion of the thyroid causes an arrest of skeletal development, and, 

 if it take place early, the subject remains a dwarf. These, then, 

 are well-known illustrations of the regulation of function by some 

 internal glandular secretion, some enzyme or "hormone" (as 

 Bayhss and Starling call it), or "harmozone," as Gley calls it in 

 the particular case where the function regulated is that of growth, 

 with its consequent influence on form. 



Among other illustrations (which are plentiful) we have, for 

 instance the growth of the placental decidua, which Loeb has 

 shewn to be due to a substance given off by the corpus luteum 

 of the ovary, giving to the uterine tissues an abnormal capacity 

 for growth, which in turn is called into action by the contact of 

 the ovum, or even of any foreign body. And various sexual 

 characters, such as the plumage, comb and spurs of the cock, 

 are believed in like manner to arise in response to some particular 

 internal secretion. When the source of such a secretion is removed 

 by castration, well-known morphological changes take place in 

 various animals; and when a converse change takes place, the 

 female acquires, in greater or less degree, characters which are 



* Amer. J. of Physiol, x, 1904. f C'.J?. cxxi, cxxii, 1895-96. 



