THE PITUITARY 



349 



not constant, and, when present, it is not abolished by section 

 of the vagi or the action of atropine. It is, therefore, of 

 peripheral origin, and is not due to the same cause as the 

 inhibition which often accompanies the action of adrenin, and 

 is brought about by an action on the car dio -inhibitory mechan- 

 ism in the bulb. 

 This action of pituitary extracts upon the heart and blood- 



FIG. 96. Effect upon the arterial pressure and intestinal volume of intra- 

 venous injection of decoction of infundibular body. Cat under morphine 

 and curare. The time of marking indicates five seconds. 



vessels is a special case of their action upon most of the involun- 

 t.ary muscles. The rise of blood-pressure already referred to 

 is due to constriction of many of the bloodvessels of the body, 

 combined with augmentation of the heart-beat. 1 



With large doses, the depressor effect may be so marked as 

 to mask the usual subsequent rise. 



1 Paton and Watson state that in the duck there is dilation of vessels and 

 not constriction. 



