668 INTERNAL SECRETION ENDOCRINE GLANDS 



nervous portion of the posterior lobe. But this colloid, whatever 

 its function may be, is very different from that of the thyroid 

 alveoli, for the (sheep's) pituitary contains no iodine after extir- 

 pation of the thyroid any more than before (Simpson and 

 Hunter). And in man pathological changes (tumours) in the 

 pituitary body are associated, not with myxcedema, or other 

 disease connected with changes in the thyroid, but frequently with 

 another condition, called acromegaly, in which the bones of the 

 limbs and face, especially the hands and feet and the lower jaw, 

 become hypertrophied. 



Another condition often associated with tumours of the pituitary 

 is gigantism a condition occurring before the normal growth of 

 the bones is completed, and resulting in a great increase in the 

 length of the bones both in the limbs and the trunk. 



Action of Intravenous Injection of Extracts of the Pituitary. 

 The effects on the vascular system of intravenous injection of 

 extracts of the pituitary gland are also very different from those 

 caused by thyroid extracts. The posterior lobe, or infundibular 

 body, including the pars intermedia, contains two active substances, 

 one pressor and the other depressor. The former is soluble in salt 

 solution, but insoluble in absolute alcohol and ether; while the 

 latter is soluble in salt solution as well as in alcohol and ether. The 

 pressor substance (obtained in fairly pure form in the preparation 

 called pituitrin, and in still greater concentration in a preparation 

 to which the name hypophysin has been given) causes a rise of 

 blood-pressure, due partly to constriction of the arterioles and 

 partly to an increase in the force of the heart-beat, both of which 

 are brought about by direct action. This rise of pressure lasts for 

 a considerable time, and is sometimes accompanied by a slowing 

 of the heart. A second dose injected before the effect of the first 

 has passed off is inactive ; and this distinguishes the pituitary from 

 the suprarenal extract. Associated with the pressor effect is an 

 increase in the flow of the urine. Whether this is due to a separate 

 diuretic substance, as some maintain, has not been definitely settled. 



Indeed, the factors on which the diuretic action depends are 

 complex, and sometimes in spite of an increase of general arterial 

 pressure, and of the volume of the kidney, there is no increased flow of 

 urine. In diabetes insipidus pituitrin has been found to produce pre- 

 cisely the opposite effect namely, diminution in the excessive urinary 

 flow. The pressor substance, unlike adrenalin, directly stimulates 

 smooth muscle fibres (especially the arteries, uterus, and spleen) irrespec- 

 tive of their innervation ^Dale). 



Many other points of difference exist between the pressor principles 

 of the infundibular body and the adrenal medulla. For example, 

 pituitrin constricts the pupil and diminishes the flow of saliva from the 

 submaxillary gland, whereas adrenalin dilates the pupil and causes an 

 increased flow of saliva. Hypophysin and other preparations of the 

 posterior lobe have been employed to stimulate the uterine contractions 

 in obstetrical practice, but their use does not seem to be free from 



