Chap. 15 



CHEMICAL REGULATION ENDOCRINE GLANDS 



273 



Fig. 15.15. The effect of extract of pars anterior of the pituitary upon the 

 growth of dogs. Normal dog and giant of the same litter that has been treated 

 with injections of the extract of the gland. (From The Living Body, Copyrighted 

 1952 by Henry Holt and Company. Reprinted with their permission.) 



intermedia can be completely suppressed while the remainder of the pituitary 

 continues to develop. In consequence the tadpoles will metamorphose into 

 frogs with silvery-colored skin. 



Regarding the relation of the pituitary to color, it is to be remembered that 

 adrenalin also concentrates the pigment in amphibian melanophores. If one 

 cubic centimeter of a solution of one part adrenalin to 10,000 parts of water 

 is injected into the dorsal lymph space of the leopard frog (Rana pipiens), 

 it will begin to turn pale in ten minutes and shortly afterward will become 

 thoroughly pallid, remaining so for a day or two. 



Functions of the Pars Tuberalis. The function of the pars tuberalis in man 

 and other vertebrates is unknown. 



Functions of the Pars Nervosa. The pars nervosa stores and releases at 

 least two hormones, pitressin and pitocin, often included together as pituitrin 

 (Table 15.1), both probably produced by neurosecretory cells of the 

 hypothalamus of the brain. Pitressin raises the blood pressure by directly 

 stimulating the contraction of smooth muscle in the arteries and arterioles. 

 Adrenalin achieves the same result but by the way of the autonomic (in- 

 voluntary) nervous system. Pitressin acts to conserve water in the body. 

 When animals are kept on short water rations there is so much antidiuretic 

 substance secreted that it appears in the urine. This holding of water in the 



