FERMENT ACTION IN GENERAL 41 



ments. Analogous effects are produced by every living organ- 

 ism, among animals for example, by (i) unorganized ferments 

 acting on foreign substances serving as food; (2) hormones or 

 enzymes produced by some portion of an animal and acting 

 upon some entirely different portion of the same animal; (3) 

 endoenzymes acting within the cells of the body upon the mo- 

 lecular constitution of living protoplasm. 



The first type is illustrated by the digestive ferments which 

 convert insoluble carbohydrates into soluble sugars and solid 

 proteids into soluble proteids, or those which cause fats to 

 emulsify. These are always formed by the living organism 

 and act upon substances foreign to the organism and taken in 

 as food. 



Hormones. The second type of enzyme action, that of hor- 

 mones, is extremely difficult to study and facts regarding it 

 have come to light only recently. A good example is the 

 enzyme secretin in man which causes the pancreas cells to 

 secrete the digestive ferments of the pancreatic juice. This 

 secretin is formed after contact of the acidified contents of the 

 stomach with the mucous membrane of the small intestine. 

 The acid food stuffs do not stimulate nerves which start secre- 

 tion in the pancreas, but they act upon a zymogen substance 

 formed in the cells of the mucous membrane, transforming this 

 zymogen into the enzyme secretin which reaches the pancreas 

 through the blood and there stimulates the pancreas cells 

 to secrete. Other hormones are responsible for many of the 

 phenomena of growth and differentiation and possibly they 

 play an important part in early development of the individual, 

 even fertilization of the egg as shown by the recent work of F. R. 

 Lillie may involve enzyme action. Again, there is strong reason 

 to suppose that secondary sexual characteristics are developed 

 at maturity through the action of hormones secreted by the 

 reproductive glands into the blood. A close relation exists 

 also between the glandular patches known as the corpora lutea 

 on the mammalian ovary, and fixation of the fertilized eggs to 

 the wall of the uterus. If these small glands are removed the 

 developing egg will not attach at all, and it is supposed that a 



