§4.2 ENDOCRINE GLANDS 131 



GEN in the blood, such as are present towards the end of hictation 

 or at the renewal of the oestrus cycle (Cowie and FoUey, 1955). 

 It is possible that the nervous system plays a part in the control of 

 prolactin secretion, but there is less evidence for a psychological 

 control over this secretion than there is for oxytocin (Fig. 3-7). 



4.14 SKIN GLANDS 



Amphibia. The skin of amphibians is kept moist in air by the 

 secretion of mucus from epidermal glands, which respond to the 

 presence of adrenaline, at least in pharmacological doses of a 

 mammalian preparation. The glands have a sympathetic nerve 

 supply, and it has not been shown that the hormone plays any part 

 in their physiological control. Under experimental conditions it is 

 possible that adrenaline contracts muscles round the glands rather 

 than stimulating secretion (Wastl, 1922). The same is probably 

 true of neurohypophysial extracts which cause an outflow of 

 secretion from the skin of Xenopus (Bastian and Zarrow, 1954). 



Mammalia. In the cat. Fells, as in man, the sweat glands in the 

 skin respond to the peculiar cholinergic stimulation supplied by 

 their sympathetic nerves; they therefore do not respond to 

 adrenaline in the blood as do other effectors, supplied by the more 

 usual adrenergic sympathetic nerves. In the horse, Equus, and 

 sheep, Ovis, the sweat glands respond to adrenaline by secretion, 

 as the mucus glands do in amphibians (fide Winton and Bayliss, 

 1955). 



4.2 Endocrine glands 

 The endocrine glands, like their exocrine counterparts, are 

 effector organs, although the fact that their secretion passes into 

 the blood, instead of appearing in a duct, makes their action less 

 apparent. The hormones, which in many cases stimulate their 

 secretion, therefore fall within the kinetic group. Since, however, 

 a hormone which causes the secretion of another hormone has 

 some peculiarities, it is convenient to distinguish it as an endo- 

 crinokinetic hormone, or one that is able to activate an endocrine 

 gland.* These hormones have sometimes been referred to as 



* "Glandotrope Wirkung" has been used to express this activity in 

 German (Karlson, 1956); but there is no accepted English term. 



