HORMONES 



injurious agents either do not, as in the case of sugar or thyroid extracts, 

 produce diabetes or else do so, as in the case of anteropituitary extracts, 

 only if much higher doses are used. In most instances the secretion of 

 the hormones is governed by humoral factors, while the nervous factors 

 play only an accessory, dispensable role. Thus, denervation of pancreas, 

 thyroid, adrenal cortex, or gonads does not produce any insufficiency 

 of their endocrine functions. Sometimes it is found that the nervous 

 action makes the secretory regulation somewhat quicker and more 

 precise, as in the case of insulin secretion. 



There are cases, however, in which the nervous regulation is 

 important. Thus the splanchnic nerves exert a tonic and emergency 

 action upon adrenalin secretion and their section reduces it to traces. 

 The supraoptic nucleus governs secretion of the antidiuretic hormone of 

 the neurohypophysis and section of the supraoptic neurohypophysial 

 fibers is followed by insipid polyuria. Stimulation by light or desicca- 

 tion inhibits the melanic-expanding secretion of the pars intermedia 

 of the hypophysis through the medium of the nervous system. After 

 cutting the pituitary stalk, the anteropituitary secretions are produced 

 in sufhcient amount so that, generally, the thyroid, adrenal, and gonads 

 are not modified. But there is no increase in the secretion in cases of 

 emergency; and in animals with the pituitary stalk cut ovulation is no 

 longer produced by mating {e. g., doe), embracing (e. g.,-toad), or vision 

 (e. g., dove) as in normal animals. Intense light can induce the secre- 

 tion of enough hypophysary gonadotropins to produce hypertrophy of 

 the gonads when they are in the atrophic condition of winter rest. 

 Cold no longer exerts its action on ovarian cycles or upon thyroid or 

 adrenal cortex when the pituitary stalk has been cut in rats. Certain 

 hypothalmic injuries may decrease the secretion of either all or some of 

 the pituitary gonadotropins. 



REGUL.\TION OF COMPLEX EQUILIBRIA 



The individual regulation of each gland is at the same time 

 submitted to more ample regulations which are often reciprocal. Thus, 

 the blood sugar level is maintained constant in spite of the coexisting 

 secretions which tend to produce either hypoglycemia, such as insulin, 

 or hyperglycemia, such as those of the hypophysis and adrenal glands. 

 There exists, therefore, a functional equilibrium of the secretion of each 

 endocrine gland and, at the same time, a functional equilibrium of all 



