54: GLANDS IN HEALTH AND DISEASE 



to Howell, the physiologist at Johns Hopkins, to 

 prove three years later that the effect was due to 

 the posterior lobe alone. 



While there are resemblances between the action 

 of adrenaline and that of the hormone in the pos- 

 terior lobe of the pituitary, there are also some 

 striking differences. For example, the action of 

 the pituitary hormone is apt to be of a more pro- 

 longed nature. Again, a second injection of 

 adrenaline repeats the action of a first injection; 

 a second injection of the pituitary hormone may 

 reverse the action of a first injection. There may 

 actually be a decrease, instead of an increase in 

 blood pressure. Or again, on the arteries of the 

 kidney the two behave diametrically opposite: 

 adrenaline constricts them and pituitary hormone 

 (which we shall refer to as "pituitrin," and to 

 which we shall refer subsequently) dilates them. 

 Pituitrin, indeed, causes quite a remarkable in- 

 crease in urinary flow, and has established itself 

 as a useful diuretic (a substance that increases the 

 secretion of urine). 



Properties of pituitrin. The action of pituitrin 

 on the flow of milk from the mammary gland is 

 no less striking than its property as a diuretic, to 

 which reference has just been made. It does not 

 seem, from the experiments conducted, that the 

 pituitrin actually increases the quantity of milk 

 secreted; rather, it accelerates the discharge once 



