568 A MANUAL OF PHYSIOLOGY 



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 ex- 

 tirpation 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 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 in- 

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



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 in- 

 fundibular 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 causes a 

 great 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. As- 

 sociated 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. The pressor 

 substance, unlike adrenalin, directly stimulates smooth muscle 

 fibres (especially the arteries, uterus, and spleen) irrespective 

 of their innervation (Dale). The depressor substance produces 

 a marked fall of blood-pressure, even when it is injected during 

 the rise of pressure caused by an injection of the pressor sub- 

 stance. The anterior lobe, or hypophysis, also contains a de- 

 pressor substance. Intravenous injection of a saline extract 

 causes a distinct fall of blood-pressure, accompanied usually by 

 acceleration and weakening of the heart (Fig. 191). A second 

 injection immediately following the first produces no change in the 

 pressure. But extracts of many organs, including the nervous 

 tissues, produce a similar fall of pressure, and there is no evidence 

 that the depressor substance of the anterior lobe is specific to 

 the pituitary (W. W. Hamburger). 



